diff --git a/CMakeLists.txt b/CMakeLists.txt
index fba2dff66e..5022dd05c0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -35,8 +35,8 @@ endif()
 
 option(INSTALL_SYSTEMD_UNITS "Install TigerVNC systemd units" ON)
 
-if(MSVC)
-  message(FATAL_ERROR "TigerVNC cannot be built with Visual Studio.  Please use MinGW")
+if(MSVC AND NOT ALLOW_MSVC_EXPERIMENTAL)
+  message(FATAL_ERROR "TigerVNC cannot be built with Visual Studio.  Please use MinGW (or pass -DALLOW_MSVC_EXPERIMENTAL=ON to try anyway)")
 endif()
 
 if(NOT BUILD_TIMESTAMP)
@@ -67,27 +67,40 @@ set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -D_DEBUG")
 set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -D_DEBUG")
 
 # Enable debug friendly optimizations for debug builds
-set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -Og")
-set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -Og")
-
-# Make sure we get a sane C and C++ version
-set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu99")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
-
-# Tell the compiler to be stringent
-add_compile_definitions(_FORTIFY_SOURCE=2)
-set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wformat=2 -Wvla")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wformat=2 -Wvla")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wzero-as-null-pointer-constant")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wsuggest-override")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wshadow")
-# Make sure we catch these issues whilst developing
-set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -Werror")
-set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -Werror")
-# clang doesn't support format_arg, which breaks this warning
-if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-format-nonliteral -Wno-format-security")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-format-nonliteral -Wno-format-security")
+# (GCC/Clang-only spelling; MSVC's own /RTC1 default conflicts with it — see
+# "D8016: '/RTC1' and '/Og' command-line options are incompatible")
+if(NOT MSVC)
+  set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -Og")
+  set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -Og")
+else()
+  # cl.exe rejects every GNU spelling above, so MSVC would otherwise get
+  # no standard flag at all and fall back to its default -- which is too
+  # old for the inline variables in SSecurityRSAAES.cxx.
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /std:c++17")
+endif()
+
+# These are GCC/Clang-only flag spellings; MSVC's cl.exe rejects them outright
+# (e.g. "D8021: invalid numeric argument '/Wextra'"), so keep the whole GNU-style
+# stringency stanza out of MSVC builds and rely on CMake's own MSVC defaults.
+if(NOT MSVC)
+  # Make sure we get a sane C and C++ version
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu99")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
+  # Tell the compiler to be stringent
+  add_compile_definitions(_FORTIFY_SOURCE=2)
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wformat=2 -Wvla")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wformat=2 -Wvla")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wzero-as-null-pointer-constant")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wsuggest-override")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wshadow")
+  # Make sure we catch these issues whilst developing
+  set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -Werror")
+  set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -Werror")
+  # clang doesn't support format_arg, which breaks this warning
+  if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-format-nonliteral -Wno-format-security")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-format-nonliteral -Wno-format-security")
+  endif()
 endif()
 
 option(ENABLE_ASAN "Enable address sanitizer support" OFF)
@@ -103,8 +116,12 @@ if(ENABLE_TSAN AND NOT WIN32 AND NOT APPLE AND CMAKE_SIZEOF_VOID_P MATCHES 8)
 endif()
 
 if(MSVC)
-  # undef min and max macro
-  target_compile_definitions(rfb PRIVATE NOMINMAX)
+  # undef min and max macro -- global, not per-target: the "rfb" target
+  # doesn't exist yet at this point in the file (add_subdirectory(common)
+  # runs later), so target_compile_definitions(rfb ...) here always failed;
+  # this MSVC branch was untestable before the hard MSVC gate above was
+  # relaxed, so the ordering bug was never caught.
+  add_compile_definitions(NOMINMAX)
 endif()
 
 if(NOT DEFINED BUILD_WINVNC)
@@ -121,6 +138,12 @@ endif()
 # Minimum version is Windows 7
 if(WIN32)
   add_definitions(-D_WIN32_WINNT=0x0601)
+  # Without this, <windows.h> pulls in the legacy <winsock.h>, which then
+  # conflicts with <winsock2.h> wherever both end up included in the same
+  # translation unit regardless of include order (duplicate struct/function
+  # definitions with "different linkage"). MinGW builds never hit this since
+  # mingw's own <windows.h> already defines this by default.
+  add_definitions(-DWIN32_LEAN_AND_MEAN)
 endif()
 
 # Legacy macros (macOS 10.12 and older) conflict with our code
@@ -185,10 +208,6 @@ trioption(ENABLE_H264 "Enable H.264 RFB encoding")
 if(ENABLE_H264)
   if(WIN32)
     set(HAVE_H264 1)
-
-    set(CMAKE_REQUIRED_LIBRARIES ole32 mfplat mfuuid wmcodecdspuuid)
-    check_variable_exists(CLSID_VideoProcessorMFT HAVE_VIDEO_PROCESSOR_MFT)
-    set(CMAKE_REQUIRED_LIBRARIES)
   else()
     if(ENABLE_H264 STREQUAL "AUTO")
       find_package(AVCodec)
@@ -289,7 +308,9 @@ if(BUILD_VIEWER)
   endif()
 
   if(FLTK_FOUND)
-    set(CMAKE_REQUIRED_FLAGS "-Wno-error")
+    if(NOT MSVC)
+      set(CMAKE_REQUIRED_FLAGS "-Wno-error")
+    endif()
     set(CMAKE_REQUIRED_INCLUDES ${FLTK_INCLUDE_DIR})
     set(CMAKE_REQUIRED_LIBRARIES ${FLTK_LIBRARIES})
 
@@ -439,12 +460,15 @@ include(cmake/StaticBuild.cmake)
 
 add_subdirectory(common)
 
-if(WIN32)
-  add_subdirectory(win)
-else()
-  # No interest in building x related parts on Apple
-  if(NOT APPLE)
-    add_subdirectory(unix)
+option(BUILD_SERVER "Build the platform-specific VNC server components" ON)
+if(BUILD_SERVER)
+  if(WIN32)
+    add_subdirectory(win)
+  else()
+    # No interest in building x related parts on Apple
+    if(NOT APPLE)
+      add_subdirectory(unix)
+    endif()
   endif()
 endif()
 
diff --git a/common/core/Configuration.cxx b/common/core/Configuration.cxx
index 234e112f96..571162f006 100644
--- a/common/core/Configuration.cxx
+++ b/common/core/Configuration.cxx
@@ -36,6 +36,7 @@
 #include <core/Configuration.h>
 #include <core/LogWriter.h>
 #include <core/i18n.h>
+#include <core/os.h>
 #include <core/string.h>
 
 #include <rdr/HexOutStream.h>
diff --git a/common/core/LogWriter.cxx b/common/core/LogWriter.cxx
index 4490c874d7..7b0e17a665 100644
--- a/common/core/LogWriter.cxx
+++ b/common/core/LogWriter.cxx
@@ -26,6 +26,7 @@
 #include <string.h>
 
 #include <core/Configuration.h>
+#include <core/os.h>
 #include <core/LogWriter.h>
 #include <core/i18n.h>
 #include <core/string.h>
diff --git a/common/core/LogWriter.h b/common/core/LogWriter.h
index b247bbec46..646b050e6e 100644
--- a/common/core/LogWriter.h
+++ b/common/core/LogWriter.h
@@ -25,6 +25,7 @@
 
 #include <core/Configuration.h>
 #include <core/Logger.h>
+#include <core/compiler.h>
 
 // Each log writer instance has a unique textual name,
 // and is attached to a particular Log instance and
@@ -32,13 +33,13 @@
 
 #define DEF_LOGFUNCTION(name, level) \
   inline void v##name(const char* fmt, va_list ap) \
-    __attribute__((__format__ (__printf__, 2, 0))) \
+    CORE_FORMAT_PRINTF(2, 0) \
   { \
     if (m_log && (level <= m_level))        \
       m_log->write(level, m_name, fmt, ap); \
   } \
   inline void name(const char* fmt, ...) \
-    __attribute__((__format__ (__printf__, 2, 3))) \
+    CORE_FORMAT_PRINTF(2, 3) \
   { \
     if (m_log && (level <= m_level)) {     \
       va_list ap; va_start(ap, fmt);       \
@@ -61,7 +62,7 @@ namespace core {
     int getLevel(void) { return m_level; }
 
     inline void write(int level, const char* format, ...)
-      __attribute__((__format__ (__printf__, 3, 4)))
+      CORE_FORMAT_PRINTF(3, 4)
     {
       if (m_log && (level <= m_level)) {
         va_list ap;
diff --git a/common/core/Logger.cxx b/common/core/Logger.cxx
index bb494acc7b..e506417538 100644
--- a/common/core/Logger.cxx
+++ b/common/core/Logger.cxx
@@ -26,6 +26,7 @@
 #include <stdio.h>
 #include <string.h>
 
+#include <core/os.h>
 #include <core/Logger.h>
 #include <core/LogWriter.h>
 #include <core/i18n.h>
diff --git a/common/core/Logger.h b/common/core/Logger.h
index 5291915f80..e81787d559 100644
--- a/common/core/Logger.h
+++ b/common/core/Logger.h
@@ -24,6 +24,8 @@
 #include <stdarg.h>
 #include <stdio.h>
 
+#include <core/compiler.h>
+
 // Each log writer instance has a unique textual name,
 // and is attached to a particular Logger instance and
 // is assigned a particular log level.
@@ -46,7 +48,7 @@ namespace core {
 
     virtual void write(int level, const char *logname, const char *text) = 0;
     void write(int level, const char *logname, const char* format, va_list ap)
-        __attribute__((__format__ (__printf__, 4, 0)));
+        CORE_FORMAT_PRINTF(4, 0);
 
     // -=- Register a logger
 
diff --git a/common/core/Logger_file.h b/common/core/Logger_file.h
index 6bce3e2df5..e7080d20ef 100644
--- a/common/core/Logger_file.h
+++ b/common/core/Logger_file.h
@@ -25,6 +25,7 @@
 #include <limits.h>
 
 #include <core/Logger.h>
+#include <core/os.h>
 
 namespace core {
 
diff --git a/common/core/Rect.h b/common/core/Rect.h
index e4cb1634b7..ec9b142901 100644
--- a/common/core/Rect.h
+++ b/common/core/Rect.h
@@ -23,6 +23,8 @@
 
 #include <algorithm>
 
+#include <core/compiler.h>
+
 namespace core {
 
   // core::Point
@@ -38,15 +40,15 @@ namespace core {
     Point() : x(0), y(0) {}
     Point(int x_, int y_) : x(x_), y(y_) {}
     inline Point negate() const
-      __attribute__ ((warn_unused_result))
+      CORE_WARN_UNUSED_RESULT
       {return Point(-x, -y);}
     inline bool operator==(const Point &p) const {return x==p.x && y==p.y;}
     inline bool operator!=(const Point &p) const {return x!=p.x || y!=p.y;}
     inline Point translate(const Point &p) const
-      __attribute__ ((warn_unused_result))
+      CORE_WARN_UNUSED_RESULT
       {return Point(x+p.x, y+p.y);}
     inline Point subtract(const Point &p) const
-      __attribute__ ((warn_unused_result))
+      CORE_WARN_UNUSED_RESULT
       {return Point(x-p.x, y-p.y);}
     int x, y;
   };
@@ -70,7 +72,7 @@ namespace core {
       tl.x = x; tl.y = y; br.x = x+w; br.y = y+h;
     }
     inline Rect intersect(const Rect &r) const
-      __attribute__ ((warn_unused_result))
+      CORE_WARN_UNUSED_RESULT
     {
       Rect result;
       result.tl.x = std::max(tl.x, r.tl.x);
@@ -80,7 +82,7 @@ namespace core {
       return result;
     }
     inline Rect union_boundary(const Rect &r) const
-      __attribute__ ((warn_unused_result))
+      CORE_WARN_UNUSED_RESULT
     {
       if (r.is_empty()) return *this;
       if (is_empty()) return r;
@@ -92,7 +94,7 @@ namespace core {
       return result;
     }
     inline Rect translate(const Point &p) const
-      __attribute__ ((warn_unused_result))
+      CORE_WARN_UNUSED_RESULT
     {
       return Rect(tl.translate(p), br.translate(p));
     }
diff --git a/common/core/Region.h b/common/core/Region.h
index 729f14754a..87b2458e69 100644
--- a/common/core/Region.h
+++ b/common/core/Region.h
@@ -25,6 +25,7 @@
 #include <vector>
 
 #include <core/Rect.h>
+#include <core/compiler.h>
 
 struct pixman_region16;
 
@@ -58,11 +59,11 @@ namespace core {
     // the following three operations return a new region:
 
     Region intersect(const Region& r) const
-      __attribute__ ((warn_unused_result));
+      CORE_WARN_UNUSED_RESULT;
     Region union_(const Region& r) const
-      __attribute__ ((warn_unused_result));
+      CORE_WARN_UNUSED_RESULT;
     Region subtract(const Region& r) const
-      __attribute__ ((warn_unused_result));
+      CORE_WARN_UNUSED_RESULT;
 
     bool operator==(const Region& b) const;
     bool operator!=(const Region& b) const;
diff --git a/common/core/Timer.cxx b/common/core/Timer.cxx
index e50792cde6..698b39575c 100644
--- a/common/core/Timer.cxx
+++ b/common/core/Timer.cxx
@@ -24,12 +24,17 @@
 #endif
 
 #include <stdio.h>
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 #include <algorithm>
 
 #include <core/LogWriter.h>
 #include <core/Timer.h>
+#include <core/os.h>
 #include <core/time.h>
 
 using namespace core;
diff --git a/common/core/Timer.h b/common/core/Timer.h
index cde672b24c..10b0c18237 100644
--- a/common/core/Timer.h
+++ b/common/core/Timer.h
@@ -21,7 +21,11 @@
 #define __CORE_TIMER_H__
 
 #include <list>
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 namespace core {
 
diff --git a/common/core/compiler.h b/common/core/compiler.h
new file mode 100644
index 0000000000..5eded87a43
--- /dev/null
+++ b/common/core/compiler.h
@@ -0,0 +1,37 @@
+/* Copyright 2026 jose-pr <jose-pr@coqui.dev>
+ *
+ * This is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this software; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
+ * USA.
+ */
+
+#ifndef __CORE_COMPILER_H__
+#define __CORE_COMPILER_H__
+
+/*
+ * A handful of GCC/Clang-only attributes have no MSVC equivalent; these
+ * macros expand to the attribute where supported and to nothing otherwise.
+ */
+#if defined(__GNUC__) || defined(__clang__)
+#define CORE_FORMAT_PRINTF(fmt_idx, args_idx) \
+  __attribute__((__format__ (__printf__, fmt_idx, args_idx)))
+#define CORE_FORMAT_ARG(idx) __attribute__ ((format_arg (idx)))
+#define CORE_WARN_UNUSED_RESULT __attribute__ ((warn_unused_result))
+#else
+#define CORE_FORMAT_PRINTF(fmt_idx, args_idx)
+#define CORE_FORMAT_ARG(idx)
+#define CORE_WARN_UNUSED_RESULT
+#endif
+
+#endif // __CORE_COMPILER_H__
diff --git a/common/core/i18n.cxx b/common/core/i18n.cxx
index a75b766739..4a17750894 100644
--- a/common/core/i18n.cxx
+++ b/common/core/i18n.cxx
@@ -32,6 +32,7 @@
 #include <Carbon/Carbon.h>
 #endif
 
+#include <core/os.h>
 #include <core/i18n.h>
 
 // Restore original functions
@@ -130,17 +131,38 @@ static void initTranslations()
   bind_textdomain_codeset("libc", "UTF-8");
 }
 
+/*
+ * When ENABLE_NLS is off, gettext.h's own dgettext/dcgettext/dngettext/
+ * dcngettext fallbacks are plain macros (not real functions), and those
+ * macros were already permanently clobbered by core/i18n.h's earlier
+ * "#define dgettext dgettext_rfb"-style aliasing (used to redirect the
+ * rest of the codebase's calls here) -- a #undef can't restore a macro's
+ * prior definition, only remove the current one. So with NLS disabled
+ * there is nothing left upstream to call into; implement the same
+ * pass-through semantics gettext.h itself would have, directly.
+ */
+
 const char *dgettext_rfb(const char *domainname, const char *msgid)
 {
   initTranslations();
+#if defined ENABLE_NLS && ENABLE_NLS
   return dgettext(domainname, msgid);
+#else
+  (void)domainname;
+  return msgid;
+#endif
 }
 
 const char *dcgettext_rfb(const char *domainname, const char *msgid,
                           int category)
 {
   initTranslations();
+#if defined ENABLE_NLS && ENABLE_NLS
   return dcgettext(domainname, msgid, category);
+#else
+  (void)domainname; (void)category;
+  return msgid;
+#endif
 }
 
 const char *dngettext_rfb(const char *domainname, const char *msgid,
@@ -148,7 +170,12 @@ const char *dngettext_rfb(const char *domainname, const char *msgid,
                           unsigned long int n)
 {
   initTranslations();
+#if defined ENABLE_NLS && ENABLE_NLS
   return dngettext(domainname, msgid, msgid_plural, n);
+#else
+  (void)domainname;
+  return (n == 1) ? msgid : msgid_plural;
+#endif
 }
 
 const char *dcngettext_rfb(const char *domainname, const char *msgid,
@@ -156,7 +183,12 @@ const char *dcngettext_rfb(const char *domainname, const char *msgid,
                            unsigned long int n, int category)
 {
   initTranslations();
+#if defined ENABLE_NLS && ENABLE_NLS
   return dcngettext(domainname, msgid, msgid_plural, n, category);
+#else
+  (void)domainname; (void)category;
+  return (n == 1) ? msgid : msgid_plural;
+#endif
 }
 
 const char *pgettext_rfb(const char *domain,
diff --git a/common/core/i18n.h b/common/core/i18n.h
index 83c05d9781..11a06bd67c 100644
--- a/common/core/i18n.h
+++ b/common/core/i18n.h
@@ -58,6 +58,8 @@ extern int swprintf (wchar_t *, size_t, const wchar_t *, ...)
   /* __attribute__((__format__ (__wprintf__, 3, 4))) */;
 #endif
 
+#include <core/compiler.h>
+
 #define _(String) gettext (String)
 #define C_(Context, String) pgettext (Context, String)
 #define N_(String) gettext_noop (String)
@@ -81,31 +83,31 @@ extern "C" {
 #endif
 
 const char *dgettext_rfb(const char *domainname, const char *msgid)
-                         __attribute__ ((format_arg (2)));
+                         CORE_FORMAT_ARG(2);
 const char *dcgettext_rfb(const char *domainname, const char *msgid,
                           int category)
-                          __attribute__ ((format_arg (2)));
+                          CORE_FORMAT_ARG(2);
 const char *dngettext_rfb(const char *domainname, const char *msgid,
                           const char *msgid_plural,
                           unsigned long int n)
-                          __attribute__ ((format_arg (2)))
-                          __attribute__ ((format_arg (3)));
+                          CORE_FORMAT_ARG(2)
+                          CORE_FORMAT_ARG(3);
 const char *dcngettext_rfb(const char *domainname, const char *msgid,
                            const char *msgid_plural,
                            unsigned long int n, int category)
-                          __attribute__ ((format_arg (2)))
-                          __attribute__ ((format_arg (3)));
+                          CORE_FORMAT_ARG(2)
+                          CORE_FORMAT_ARG(3);
 
 const char *pgettext_rfb(const char *domain,
                          const char *msg_ctxt_id, const char *msgid,
                          int category)
-                         __attribute__ ((format_arg (3)));
+                         CORE_FORMAT_ARG(3);
 const char *npgettext_rfb(const char *domain,
                           const char *msg_ctxt_id, const char *msgid,
                           const char *msgid_plural,
                           unsigned long int n, int category)
-                          __attribute__ ((format_arg (3)))
-                          __attribute__ ((format_arg (4)));
+                          CORE_FORMAT_ARG(3)
+                          CORE_FORMAT_ARG(4);
 
 #ifdef __cplusplus
 }
diff --git a/common/core/os.h b/common/core/os.h
new file mode 100644
index 0000000000..6177acffe9
--- /dev/null
+++ b/common/core/os.h
@@ -0,0 +1,134 @@
+/* Copyright 2026 jose-pr <jose-pr@coqui.dev>
+ *
+ * This is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this software; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
+ * USA.
+ */
+
+#ifndef __CORE_OS_H__
+#define __CORE_OS_H__
+
+/*
+ * MSVC lacks a number of POSIX APIs that this project's previous Windows
+ * toolchain (mingw, a GCC/glibc-compatible environment) provided
+ * transparently. Centralize the portable equivalents/shims here rather
+ * than scattering per-file fixes.
+ */
+#ifdef _WIN32
+
+#include <stdlib.h> // _MAX_PATH
+#include <string.h> // _stricmp, _strnicmp
+#include <winsock2.h> // struct timeval, FILETIME
+
+#ifndef PATH_MAX
+#define PATH_MAX _MAX_PATH
+#endif
+
+/* mingw is a GCC/glibc-compatible environment that provides all of the
+ * below for real, just from the POSIX headers rather than the ones a
+ * Windows source file would otherwise include. Pull those in here so
+ * callers get the genuine declarations, and shim only for MSVC -- both
+ * halves matter, as redefining them under mingw collides with the real
+ * ones. */
+#ifndef _MSC_VER
+
+#include <strings.h> // strcasecmp, strncasecmp
+#include <sys/time.h> // gettimeofday
+#include <sys/types.h> // mode_t
+#include <libgen.h> // dirname
+#include <unistd.h> // usleep
+
+#else
+
+#define strcasecmp _stricmp
+#define strncasecmp _strnicmp
+
+typedef int mode_t;
+
+/* POSIX ssize_t: a signed size. MSVC only spells it SSIZE_T, from
+ * <basetsd.h>, which <winsock2.h> above already pulls in. */
+typedef SSIZE_T ssize_t;
+
+inline int gettimeofday(struct timeval *tv, void *)
+{
+  /* FILETIME is in 100ns intervals since 1601-01-01; convert to
+   * microseconds since the Unix epoch (1970-01-01). */
+  static const unsigned long long kEpochDiff = 116444736000000000ULL;
+  FILETIME ft;
+  unsigned long long t;
+
+  GetSystemTimeAsFileTime(&ft);
+  t = ((unsigned long long)ft.dwHighDateTime << 32) | ft.dwLowDateTime;
+  t = (t - kEpochDiff) / 10;
+
+  tv->tv_sec = (long)(t / 1000000ULL);
+  tv->tv_usec = (long)(t % 1000000ULL);
+
+  return 0;
+}
+
+/* POSIX ffs(): one plus the index of the least significant set bit, or
+ * zero if there is none. mingw supplies it from <strings.h>; MSVC has no
+ * equivalent, so map it onto the intrinsic. */
+#include <intrin.h>
+
+inline int ffs(int i)
+{
+  unsigned long bit;
+
+  if (!_BitScanForward(&bit, (unsigned long)i))
+    return 0;
+
+  return (int)bit + 1;
+}
+
+/* POSIX usleep(). Windows only offers millisecond granularity, so a
+ * sub-millisecond request rounds up to 1ms rather than to 0 -- sleeping
+ * for less than asked is the one behaviour a caller cannot correct for. */
+inline int usleep(unsigned long usec)
+{
+  Sleep((DWORD)((usec + 999) / 1000));
+  return 0;
+}
+
+/* POSIX dirname(), minimally: strip the trailing filename component,
+ * accepting both path separators since Windows paths use either. Modifies
+ * and returns its argument, matching the (permitted) in-place POSIX form. */
+inline char *dirname(char *path)
+{
+  char *slash = strrchr(path, '\\');
+  char *fwdslash = strrchr(path, '/');
+
+  if (fwdslash > slash)
+    slash = fwdslash;
+
+  if (slash == nullptr) {
+    static char dot[] = ".";
+    return dot;
+  }
+
+  if (slash == path) {
+    *(slash + 1) = '\0';
+    return path;
+  }
+
+  *slash = '\0';
+  return path;
+}
+
+#endif // _MSC_VER
+
+#endif // _WIN32
+
+#endif // __CORE_OS_H__
diff --git a/common/core/string.h b/common/core/string.h
index a67ade3b5a..af5beb2c5d 100644
--- a/common/core/string.h
+++ b/common/core/string.h
@@ -29,11 +29,13 @@
 #include <string>
 #include <vector>
 
+#include <core/compiler.h>
+
 namespace core {
 
   // Formats according to printf(), with a dynamic allocation
   std::string format(const char *fmt, ...)
-      __attribute__((__format__ (__printf__, 1, 2)));
+      CORE_FORMAT_PRINTF(1, 2);
 
   // Splits a string with the specified delimiter
   std::vector<std::string> split(const char* src,
diff --git a/common/core/time.cxx b/common/core/time.cxx
index 47a0ff8ad6..ffdedb73c6 100644
--- a/common/core/time.cxx
+++ b/common/core/time.cxx
@@ -22,8 +22,13 @@
 #endif
 
 #include <stddef.h>
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
+#include <core/os.h>
 #include <core/time.h>
 
 namespace core {
diff --git a/common/core/xdgdirs.cxx b/common/core/xdgdirs.cxx
index 2628f317b5..e6c748c5ba 100644
--- a/common/core/xdgdirs.cxx
+++ b/common/core/xdgdirs.cxx
@@ -37,10 +37,13 @@
 #include <windows.h>
 #include <wininet.h> /* MinGW needs it */
 #include <shlobj.h>
+#include <direct.h> /* _mkdir */
 #define stat _stat
-#define mkdir(path, mode) mkdir(path)
+/* MSVC only provides _mkdir (no bare mkdir symbol at all, unlike mingw) */
+#define mkdir(path, mode) _mkdir(path)
 #endif
 
+#include <core/os.h>
 #include <core/xdgdirs.h>
 
 static const char* getvncdir(bool userDir, const char *xdg_env, const char *xdg_def)
diff --git a/common/core/xdgdirs.h b/common/core/xdgdirs.h
index 0769ba8bae..7f642f1ec4 100644
--- a/common/core/xdgdirs.h
+++ b/common/core/xdgdirs.h
@@ -22,6 +22,8 @@
 
 #include <sys/stat.h>
 
+#include <core/os.h>
+
 namespace core {
 
   /*
diff --git a/common/network/TcpSocket.cxx b/common/network/TcpSocket.cxx
index 3d6f22858a..dca9cd23e4 100644
--- a/common/network/TcpSocket.cxx
+++ b/common/network/TcpSocket.cxx
@@ -39,7 +39,9 @@
 #include <ctype.h>
 #include <stdlib.h>
 #include <string.h>
+#ifndef WIN32
 #include <unistd.h>
+#endif
 
 #include <core/Configuration.h>
 #include <core/Exception.h>
diff --git a/common/rdr/BufferedInStream.cxx b/common/rdr/BufferedInStream.cxx
index 0ebbd65508..885dae4672 100644
--- a/common/rdr/BufferedInStream.cxx
+++ b/common/rdr/BufferedInStream.cxx
@@ -23,6 +23,7 @@
 
 #include <assert.h>
 
+#include <core/os.h>
 #include <core/i18n.h>
 #include <core/string.h>
 
diff --git a/common/rdr/BufferedInStream.h b/common/rdr/BufferedInStream.h
index b3d6115e08..2d4a961c69 100644
--- a/common/rdr/BufferedInStream.h
+++ b/common/rdr/BufferedInStream.h
@@ -24,7 +24,11 @@
 #ifndef __RDR_BUFFEREDINSTREAM_H__
 #define __RDR_BUFFEREDINSTREAM_H__
 
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 #include <rdr/InStream.h>
 
diff --git a/common/rdr/BufferedOutStream.cxx b/common/rdr/BufferedOutStream.cxx
index ee423eba3b..b2372b871c 100644
--- a/common/rdr/BufferedOutStream.cxx
+++ b/common/rdr/BufferedOutStream.cxx
@@ -22,6 +22,7 @@
 #include <config.h>
 #endif
 
+#include <core/os.h>
 #include <core/i18n.h>
 #include <core/string.h>
 
diff --git a/common/rdr/BufferedOutStream.h b/common/rdr/BufferedOutStream.h
index dd765dc9ed..ed18cf84e0 100644
--- a/common/rdr/BufferedOutStream.h
+++ b/common/rdr/BufferedOutStream.h
@@ -24,7 +24,11 @@
 #ifndef __RDR_BUFFEREDOUTSTREAM_H__
 #define __RDR_BUFFEREDOUTSTREAM_H__
 
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 #include <rdr/OutStream.h>
 
diff --git a/common/rdr/FdInStream.cxx b/common/rdr/FdInStream.cxx
index 25542a0149..a4be35659c 100644
--- a/common/rdr/FdInStream.cxx
+++ b/common/rdr/FdInStream.cxx
@@ -23,7 +23,6 @@
 #include <stdio.h>
 #include <string.h>
 #include <errno.h>
-#include <sys/time.h>
 #ifdef _WIN32
 #include <winsock2.h>
 #define errorNumber WSAGetLastError()
@@ -32,6 +31,7 @@
 #else
 #include <sys/types.h>
 #include <sys/socket.h>
+#include <sys/time.h>
 #include <unistd.h>
 #define errorNumber errno
 #endif
diff --git a/common/rdr/FdOutStream.cxx b/common/rdr/FdOutStream.cxx
index 416926c1ec..61efb3dd4e 100644
--- a/common/rdr/FdOutStream.cxx
+++ b/common/rdr/FdOutStream.cxx
@@ -44,6 +44,7 @@
 #include <sys/select.h>
 #endif
 
+#include <core/os.h>
 #include <core/Exception.h>
 #include <core/time.h>
 
diff --git a/common/rdr/FdOutStream.h b/common/rdr/FdOutStream.h
index d9f16efb71..f37fe97f7c 100644
--- a/common/rdr/FdOutStream.h
+++ b/common/rdr/FdOutStream.h
@@ -24,7 +24,11 @@
 #ifndef __RDR_FDOUTSTREAM_H__
 #define __RDR_FDOUTSTREAM_H__
 
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 #include <rdr/BufferedOutStream.h>
 
diff --git a/common/rfb/Congestion.cxx b/common/rfb/Congestion.cxx
index 46bae00da4..278263220c 100644
--- a/common/rfb/Congestion.cxx
+++ b/common/rfb/Congestion.cxx
@@ -39,7 +39,11 @@
 
 #include <assert.h>
 #include <string.h>
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 #ifdef __linux__
 #include <sys/ioctl.h>
@@ -50,6 +54,7 @@
 #endif
 
 #include <core/LogWriter.h>
+#include <core/os.h>
 #include <core/time.h>
 
 #include <rfb/Congestion.h>
diff --git a/common/rfb/H264WinDecoderContext.cxx b/common/rfb/H264WinDecoderContext.cxx
index 1bc7968d5c..99a80f54c0 100644
--- a/common/rfb/H264WinDecoderContext.cxx
+++ b/common/rfb/H264WinDecoderContext.cxx
@@ -36,10 +36,18 @@
 
 using namespace rfb;
 
-// Older MinGW lacks this definition
-#ifndef HAVE_VIDEO_PROCESSOR_MFT
-static GUID CLSID_VideoProcessorMFT = { 0x88753b26, 0x5b24, 0x49bd, { 0xb2, 0xe7, 0xc, 0x44, 0x5c, 0x78, 0xc9, 0x82 } };
-#endif
+/*
+ * CLSID_VideoProcessorMFT's GUID data ships in wmcodecdspuuid.lib
+ * regardless of target, but recent Windows SDKs (mfidl.h) only *declare*
+ * it when building against WINVER < _WIN32_WINNT_WINTHRESHOLD (i.e. pre-
+ * Windows-10); above that the declaration is removed from the header even
+ * though the linkable symbol still exists. Older MinGW headers never
+ * declared it either. Use our own name unconditionally instead of trying
+ * to detect header visibility (CMake's check_variable_exists only tests
+ * linkability, not header visibility, so it can't tell the two cases
+ * apart -- see CMakeLists.txt history).
+ */
+static const GUID kCLSID_VideoProcessorMFT = { 0x88753b26, 0x5b24, 0x49bd, { 0xb2, 0xe7, 0xc, 0x44, 0x5c, 0x78, 0xc9, 0x82 } };
 
 H264WinDecoderContext::H264WinDecoderContext(const core::Rect &r)
   : H264DecoderContext(r)
@@ -50,7 +58,7 @@ H264WinDecoderContext::H264WinDecoderContext(const core::Rect &r)
   if (FAILED(CoCreateInstance(CLSID_CMSH264DecoderMFT, nullptr, CLSCTX_INPROC_SERVER, IID_IMFTransform, (LPVOID*)&decoder)))
     throw std::runtime_error(_("Could not find video codec"));
 
-  if (FAILED(CoCreateInstance(CLSID_VideoProcessorMFT, nullptr, CLSCTX_INPROC_SERVER, IID_IMFTransform, (LPVOID*)&converter)))
+  if (FAILED(CoCreateInstance(kCLSID_VideoProcessorMFT, nullptr, CLSCTX_INPROC_SERVER, IID_IMFTransform, (LPVOID*)&converter)))
   {
     if (FAILED(CoCreateInstance(CLSID_CColorConvertDMO, nullptr, CLSCTX_INPROC_SERVER, IID_IMFTransform, (LPVOID*)&converter)))
     {
diff --git a/common/rfb/SSecurityRSAAES.cxx b/common/rfb/SSecurityRSAAES.cxx
index 398eff4de1..d08d670aa0 100644
--- a/common/rfb/SSecurityRSAAES.cxx
+++ b/common/rfb/SSecurityRSAAES.cxx
@@ -38,6 +38,7 @@
 #include <nettle/asn1.h>
 #include <nettle/version.h>
 
+#include <core/os.h>
 #include <core/Exception.h>
 #include <core/LogWriter.h>
 #include <core/i18n.h>
diff --git a/common/rfb/Security.cxx b/common/rfb/Security.cxx
index 58eea010b3..7841d835f7 100644
--- a/common/rfb/Security.cxx
+++ b/common/rfb/Security.cxx
@@ -27,6 +27,7 @@
 #include <stdexcept>
 
 #include <core/LogWriter.h>
+#include <core/os.h>
 #include <core/i18n.h>
 #include <core/string.h>
 
diff --git a/common/rfb/VNCServerST.h b/common/rfb/VNCServerST.h
index 07392794fe..1f79d80b26 100644
--- a/common/rfb/VNCServerST.h
+++ b/common/rfb/VNCServerST.h
@@ -24,7 +24,11 @@
 #ifndef __RFB_VNCSERVERST_H__
 #define __RFB_VNCSERVERST_H__
 
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 #include <core/Timer.h>
 
diff --git a/common/rfb/encodings.cxx b/common/rfb/encodings.cxx
index 21bd874c0d..fb03229960 100644
--- a/common/rfb/encodings.cxx
+++ b/common/rfb/encodings.cxx
@@ -22,6 +22,7 @@
 
 #include <string.h>
 
+#include <core/os.h>
 #include <core/i18n.h>
 
 #include <rfb/encodings.h>
diff --git a/tests/perf/decperf.cxx b/tests/perf/decperf.cxx
index 1ac3a535a1..6976b43fc8 100644
--- a/tests/perf/decperf.cxx
+++ b/tests/perf/decperf.cxx
@@ -31,7 +31,11 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <math.h>
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 #include <rdr/FileInStream.h>
 #include <rdr/OutStream.h>
@@ -42,6 +46,7 @@
 #include <rfb/PixelBuffer.h>
 #include <rfb/PixelFormat.h>
 
+#include <core/os.h>
 #include "util.h"
 
 // FIXME: Files are always in this format
diff --git a/tests/perf/encperf.cxx b/tests/perf/encperf.cxx
index 7eb3898407..da3de44131 100644
--- a/tests/perf/encperf.cxx
+++ b/tests/perf/encperf.cxx
@@ -35,7 +35,11 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <math.h>
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 #include <core/Configuration.h>
 
@@ -52,6 +56,7 @@
 #include <rfb/SConnection.h>
 #include <rfb/SMsgWriter.h>
 
+#include <core/os.h>
 #include "util.h"
 
 static core::IntParameter width("width", "Frame buffer width", 0);
diff --git a/tests/perf/fbperf.cxx b/tests/perf/fbperf.cxx
index 1a5b5ba713..512492c4be 100644
--- a/tests/perf/fbperf.cxx
+++ b/tests/perf/fbperf.cxx
@@ -21,7 +21,11 @@
 #endif
 
 #include <math.h>
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 #include <FL/Fl.H>
 #include <FL/Fl_Window.H>
@@ -33,6 +37,7 @@
 
 #include "../vncviewer/PlatformPixelBuffer.h"
 
+#include <core/os.h>
 #include "util.h"
 
 class TestWindow: public Fl_Window {
diff --git a/tests/unit/emulatemb.cxx b/tests/unit/emulatemb.cxx
index d59ce509d3..3f0c80e8e3 100644
--- a/tests/unit/emulatemb.cxx
+++ b/tests/unit/emulatemb.cxx
@@ -21,7 +21,11 @@
 #include <config.h>
 #endif
 
+#ifdef _WIN32
+#include <core/os.h>
+#else
 #include <unistd.h>
+#endif
 
 #include <vector>
 
diff --git a/tests/unit/gesturehandler.cxx b/tests/unit/gesturehandler.cxx
index cf2e5b6bd4..1d0c284c01 100644
--- a/tests/unit/gesturehandler.cxx
+++ b/tests/unit/gesturehandler.cxx
@@ -20,7 +20,11 @@
 #include <config.h>
 #endif
 
+#ifdef _WIN32
+#include <core/os.h>
+#else
 #include <unistd.h>
+#endif
 
 #include <vector>
 
diff --git a/vncviewer/BaseTouchHandler.cxx b/vncviewer/BaseTouchHandler.cxx
index 3100f86b98..f49d09bd19 100644
--- a/vncviewer/BaseTouchHandler.cxx
+++ b/vncviewer/BaseTouchHandler.cxx
@@ -30,6 +30,7 @@
 #include <rfb/keysymdef.h>
 
 #include "GestureHandler.h"
+#include <core/os.h>
 #include "BaseTouchHandler.h"
 
 // Sensitivity threshold for gestures
diff --git a/vncviewer/BaseTouchHandler.h b/vncviewer/BaseTouchHandler.h
index 8db658c0fd..9a30446d0e 100644
--- a/vncviewer/BaseTouchHandler.h
+++ b/vncviewer/BaseTouchHandler.h
@@ -22,7 +22,11 @@
 
 #include "GestureEvent.h"
 
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 class BaseTouchHandler {
   public:
diff --git a/vncviewer/DesktopWindow.cxx b/vncviewer/DesktopWindow.cxx
index 199b2e8118..55b0f6fec3 100644
--- a/vncviewer/DesktopWindow.cxx
+++ b/vncviewer/DesktopWindow.cxx
@@ -23,11 +23,22 @@
 
 #include <algorithm>
 
+/*
+ * MSVC only recognizes the and/or/not alternative operator tokens via this
+ * standard header; GCC/Clang support them natively and treat this as a
+ * no-op, so it's safe to include unconditionally.
+ */
+#include <ciso646>
+
 #include <assert.h>
 #include <stdio.h>
 #include <string.h>
 #include <time.h>
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
 
 #include <core/LogWriter.h>
 #include <core/i18n.h>
@@ -37,6 +48,7 @@
 #include <rfb/CMsgWriter.h>
 #include <rfb/ScreenSet.h>
 
+#include <core/os.h>
 #include "DesktopWindow.h"
 #include "OptionsDialog.h"
 #include "parameters.h"
diff --git a/vncviewer/DesktopWindow.h b/vncviewer/DesktopWindow.h
index af1b7474df..5eb936313f 100644
--- a/vncviewer/DesktopWindow.h
+++ b/vncviewer/DesktopWindow.h
@@ -24,7 +24,13 @@
 #include <map>
 #include <string>
 
+#ifdef _WIN32
+#include <winsock2.h>
+#else
 #include <sys/time.h>
+#endif
+
+#include <core/compiler.h>
 
 #include <FL/Fl_Window.H>
 
@@ -86,9 +92,9 @@ class DesktopWindow : public Fl_Window {
 
 private:
   void addOverlayTip(const char *text, ...)
-    __attribute__((__format__ (__printf__, 2, 3)));
+    CORE_FORMAT_PRINTF(2, 3);
   void addOverlayError(const char *text, ...)
-    __attribute__((__format__ (__printf__, 2, 3)));
+    CORE_FORMAT_PRINTF(2, 3);
   void addOverlay(const char *text);
   static void updateOverlay(void *data);
 
diff --git a/vncviewer/GestureHandler.cxx b/vncviewer/GestureHandler.cxx
index 2ede991b22..4b435c62b3 100644
--- a/vncviewer/GestureHandler.cxx
+++ b/vncviewer/GestureHandler.cxx
@@ -18,7 +18,13 @@
  */
 
  #ifdef HAVE_CONFIG_H
- #include <config.h>
+ /* MSVC only defines M_PI and friends when asked, and this must come
+ * before any math header. gettimeofday() comes from core/os.h. */
+#ifdef _WIN32
+#define _USE_MATH_DEFINES
+#include <core/os.h>
+#endif
+#include <config.h>
  #endif
 
 #include <assert.h>
diff --git a/vncviewer/ServerDialog.cxx b/vncviewer/ServerDialog.cxx
index 2dc2824b5f..dc34426d9a 100644
--- a/vncviewer/ServerDialog.cxx
+++ b/vncviewer/ServerDialog.cxx
@@ -23,7 +23,11 @@
 
 #include <errno.h>
 #include <algorithm>
+#ifndef WIN32
 #include <libgen.h>
+#endif
+
+#include <core/os.h>
 
 // FIXME: Workaround for FLTK including windows.h
 #ifdef WIN32
diff --git a/vncviewer/ShortcutHandler.cxx b/vncviewer/ShortcutHandler.cxx
index 05ba75fb6a..af7cfa02e0 100644
--- a/vncviewer/ShortcutHandler.cxx
+++ b/vncviewer/ShortcutHandler.cxx
@@ -25,6 +25,7 @@
 #define XK_MISCELLANY
 #include <rfb/keysymdef.h>
 
+#include <core/os.h>
 #include "ShortcutHandler.h"
 
 ShortcutHandler::ShortcutHandler() :
diff --git a/vncviewer/vncviewer.cxx b/vncviewer/vncviewer.cxx
index 20a0174b8c..410c0f9e62 100644
--- a/vncviewer/vncviewer.cxx
+++ b/vncviewer/vncviewer.cxx
@@ -30,12 +30,14 @@
 #include <signal.h>
 #include <locale.h>
 #include <fcntl.h>
-#include <unistd.h>
 #include <sys/stat.h>
 
 #ifdef WIN32
 #include <core/winerrno.h>
 #include <direct.h>
+#include <io.h> // _open_osfhandle
+#else
+#include <unistd.h>
 #endif
 
 #include <core/Exception.h>
@@ -378,20 +380,33 @@ static void usage(const char *programName)
   }
 #endif
 
+  /*
+   * MSVC rejects preprocessor directives inside a macro argument list
+   * (the _() call below); GCC/Clang tolerate it as an extension, but it's
+   * undefined behavior per the standard. Duplicate the two variants
+   * in full instead of straddling the macro call with #ifndef/#endif.
+   */
+#ifndef WIN32
   fprintf(stderr, _(
           "\n"
           "Usage: %s [parameters] [host][:displayNum]\n"
           "       %s [parameters] [host][::port]\n"
-#ifndef WIN32
           "       %s [parameters] [unix socket]\n"
-#endif
           "       %s [parameters] -listen [port]\n"
           "       %s [parameters] [.tigervnc file]\n"),
           programName, programName,
-#ifndef WIN32
           programName,
-#endif
           programName, programName);
+#else
+  fprintf(stderr, _(
+          "\n"
+          "Usage: %s [parameters] [host][:displayNum]\n"
+          "       %s [parameters] [host][::port]\n"
+          "       %s [parameters] -listen [port]\n"
+          "       %s [parameters] [.tigervnc file]\n"),
+          programName, programName,
+          programName, programName);
+#endif
 
 #if !defined(WIN32) && !defined(__APPLE__)
   fprintf(stderr, _("\n"
diff --git a/vncviewer/vncviewer.h b/vncviewer/vncviewer.h
index 44c5f53e97..74e5c75130 100644
--- a/vncviewer/vncviewer.h
+++ b/vncviewer/vncviewer.h
@@ -19,12 +19,14 @@
 #ifndef __VNCVIEWER_H__
 #define __VNCVIEWER_H__
 
+#include <core/compiler.h>
+
 #define VNCSERVERNAMELEN 256
 
 void abort_vncviewer(const char *error, ...)
-  __attribute__((__format__ (__printf__, 1, 2)));
+  CORE_FORMAT_PRINTF(1, 2);
 void abort_connection(const char *error, ...)
-  __attribute__((__format__ (__printf__, 1, 2)));
+  CORE_FORMAT_PRINTF(1, 2);
 void abort_connection_with_unexpected_error(const std::exception &);
 
 void disconnect();
diff --git a/win/rfb_win32/DeviceFrameBuffer.cxx b/win/rfb_win32/DeviceFrameBuffer.cxx
index d20b6dc764..7bc08d77cd 100644
--- a/win/rfb_win32/DeviceFrameBuffer.cxx
+++ b/win/rfb_win32/DeviceFrameBuffer.cxx
@@ -29,6 +29,7 @@
 #include <vector>
 
 #include <core/LogWriter.h>
+#include <core/os.h>
 #include <core/i18n.h>
 
 #include <rfb_win32/DeviceFrameBuffer.h>
@@ -185,9 +186,9 @@ void DeviceFrameBuffer::setCursor(HCURSOR hCursor, VNCServer* server)
       // We may not get the RGBA order we want, so shuffle things around
       int ridx, gidx, bidx, aidx;
 
-      ridx = __builtin_ffs(bi.bV5RedMask) / 8;
-      gidx = __builtin_ffs(bi.bV5GreenMask) / 8;
-      bidx = __builtin_ffs(bi.bV5BlueMask) / 8;
+      ridx = ffs(bi.bV5RedMask) / 8;
+      gidx = ffs(bi.bV5GreenMask) / 8;
+      bidx = ffs(bi.bV5BlueMask) / 8;
       // Usually not set properly
       aidx = 6 - ridx - gidx - bidx;
 
diff --git a/win/vncconfig/Authentication.h b/win/vncconfig/Authentication.h
index 3ee7b049bc..79263e2956 100644
--- a/win/vncconfig/Authentication.h
+++ b/win/vncconfig/Authentication.h
@@ -21,6 +21,10 @@
 // FIXME: The implementation should be moved to Authentication.cxx so we
 //        don't have all of these #includes polluting everything
 
+/* WIN32_LEAN_AND_MEAN keeps <windows.h> from pulling this in, and the
+ * common-dialog types below need it. mingw's headers included it
+ * transitively, which is why this was never needed before. */
+#include <commdlg.h>
 #include <windows.h>
 #include <commctrl.h>
 
diff --git a/win/winvnc/VNCServerService.cxx b/win/winvnc/VNCServerService.cxx
index 4da0a5dc08..9a8ac50745 100644
--- a/win/winvnc/VNCServerService.cxx
+++ b/win/winvnc/VNCServerService.cxx
@@ -43,7 +43,9 @@ const char* winvnc::VNCServerService::Name = "TigerVNC";
 
 // SendSAS is not available until Windows 7, and missing from MinGW
 static HMODULE sasLibrary = nullptr;
-typedef void WINAPI (*SendSAS_proto)(BOOL AsUser);
+/* The calling convention belongs on the pointer, not before it. gcc
+ * accepts the transposed form; MSVC rejects it outright. */
+typedef void (WINAPI *SendSAS_proto)(BOOL AsUser);
 static SendSAS_proto _SendSAS = nullptr;
 
 VNCServerService::VNCServerService()
diff --git a/win/wm_hooks/wm_hooks.cxx b/win/wm_hooks/wm_hooks.cxx
index 2f04b85173..4e95d69bcf 100644
--- a/win/wm_hooks/wm_hooks.cxx
+++ b/win/wm_hooks/wm_hooks.cxx
@@ -26,7 +26,22 @@
 
 #include <wm_hooks/wm_hooks.h>
 
+/* These live in a shared data section so every process the hook DLL is
+ * injected into sees one copy. gcc marks each variable with an attribute;
+ * MSVC has no per-variable equivalent, so the groups below are bracketed
+ * by data_seg pragmas instead and SHARED itself expands to nothing. The
+ * linker directive is what actually makes the segment shared -- without
+ * it the section exists but every process gets its own copy. */
+#ifdef _MSC_VER
+#pragma comment(linker, "/SECTION:shared,RWS")
+#define SHARED
+#define SHARED_BEGIN __pragma(data_seg("shared"))
+#define SHARED_END   __pragma(data_seg())
+#else
 #define SHARED __attribute__((section ("shared"), shared))
+#define SHARED_BEGIN
+#define SHARED_END
+#endif
 
 UINT WM_HK_PingThread = RegisterWindowMessage("RFB.WM_Hooks.PingThread");
 
@@ -89,6 +104,7 @@ BOOL WINAPI DllMain(HANDLE instance, ULONG reason, LPVOID /*reserved*/) {
 // -=- Display update hooks
 //
 
+SHARED_BEGIN
 DWORD hook_owner SHARED = 0;
 DWORD hook_target SHARED = 0;
 HHOOK hook_CallWndProc SHARED = nullptr;
@@ -100,6 +116,7 @@ HCURSOR cursor SHARED = nullptr;
 #ifdef _DEBUG
 UINT diagnostic_min SHARED =1;
 UINT diagnostic_max SHARED =0;
+SHARED_END
 #endif
 
 #ifdef _DEBUG
@@ -375,12 +392,14 @@ BOOL WM_Hooks_Remove(DWORD owner) {
 // -=- User input hooks
 //
 
+SHARED_BEGIN
 HHOOK hook_keyboard SHARED = nullptr;
 HHOOK hook_pointer SHARED = nullptr;
 bool enable_real_ptr SHARED = true;
 bool enable_synth_ptr SHARED = true;
 bool enable_real_kbd SHARED = true;
 bool enable_synth_kbd SHARED = true;
+SHARED_END
 
 #ifdef WH_KEYBOARD_LL
 LRESULT CALLBACK HookKeyboardHook(int nCode, WPARAM wParam, LPARAM lParam) {