diff --git a/makefile b/makefile
index 3a48e468..50dba1fe 100644
--- a/makefile
+++ b/makefile
@@ -36,6 +36,8 @@ ON_GNU_WARNING_FLAGS = -Wall \
 	-Wno-switch \
 	-Wno-unknown-pragmas \
 	-Wno-unused-private-field
+# Note that -Wno-unused-private-field may throw unrecognized option
+# error. This happened at least on GCC 8.3.0 in Rasbian Buster.
 	
 #	-Wno-inconsistent-missing-override \
 
@@ -62,6 +64,8 @@ LINK = $(CCC)
 LINKFLAGS =
 # below necessary LINKFLAGS on Linux for the UUID library
 #LINKFLAGS = -luuid
+# below necessary LINKFLAGS on Linux / Raspberry Pi 4 for UUID and atomic libraries
+#LINKFLAGS = -luuid -latomic
 
 ###############################################################
 
diff --git a/opennurbs_dimension.h b/opennurbs_dimension.h
index 4d71c71b..8058cbb3 100644
--- a/opennurbs_dimension.h
+++ b/opennurbs_dimension.h
@@ -888,9 +888,9 @@ class ON_CLASS ON_DimRadial : public ON_Dimension
 //            |
 //            |
 //            + kinkpt2
-//             \
-//              \  kinkoffset2
-//               \
+//             -
+//              -  kinkoffset2
+//               -
 //                + kinkpt1
 //                |
 //                |  kinkoffset1
diff --git a/opennurbs_lock.h b/opennurbs_lock.h
index a428c857..a30c6469 100644
--- a/opennurbs_lock.h
+++ b/opennurbs_lock.h
@@ -112,7 +112,7 @@ class ON_CLASS ON_Lock
   //         needs to have dll-interface to be used by clients of class 'ON_Lock'
   // m_lock_value is private and all code that manages m_lock_value is explicitly implemented in the DLL.
 private:
-#if defined(ON_COMPILER_CLANG)
+#if defined(ON_COMPILER_CLANG) || defined (ON_RUNTIME_LINUX_ARM)
     std::atomic<int> m_lock_value;
 #else
   std::atomic<int> m_lock_value = ON_Lock::UnlockedValue;
diff --git a/opennurbs_system_compiler.h b/opennurbs_system_compiler.h
index c03e7694..dc1d2a25 100644
--- a/opennurbs_system_compiler.h
+++ b/opennurbs_system_compiler.h
@@ -357,7 +357,6 @@
 // ON_COMPILER_GNU
 //
 */
-
 #define ON_COMPILER_GNU
 #if !defined(_GNU_SOURCE)
 #define _GNU_SOURCE
@@ -389,6 +388,13 @@
 
 #endif
 
+#if defined(__arm__)
+// GCC 8.3.0 on Raspbian (Raspberry Pi 4) needs this too
+#if !defined(ON_CLANG_CONSTRUCTOR_BUG)
+#define ON_CLANG_CONSTRUCTOR_BUG
+#endif
+#endif
+
 
 #elif defined(__BORLANDC__)
 /*
diff --git a/opennurbs_system_runtime.h b/opennurbs_system_runtime.h
index 83d1b87b..1a408a01 100644
--- a/opennurbs_system_runtime.h
+++ b/opennurbs_system_runtime.h
@@ -33,6 +33,7 @@
 //   At most one the ON_RUNTIME_* should be defined
 //
 //   ON_RUNTIME_APPLE / ON_RUNTIME_WIN / ON_RUNTIME_ANDROID
+//   ON_RUNTIME_LINUX
 //
 */
 #if (defined(__APPLE__) || defined(TARGET_OS_IPHONE) || defined(TARGET_IPHONE_SIMULATOR) || defined(__IOS__))
@@ -60,6 +61,7 @@
 #define ON_RUNTIME_LINUX
 #endif
 
+
 #endif
 /*
 //
@@ -157,7 +159,14 @@
 
 #elif defined(ON_RUNTIME_LINUX)
 
-#if defined(__x86_64__)
+#if defined(__arm__)
+#if !defined(ON_RUNTIME_LINUX_ARM)
+#define ON_RUNTIME_LINUX_ARM
+#endif
+// assume 64bit ARM (like Raspberry Pi 4)
+#define ON_64BIT_RUNTIME
+#define ON_LITTLE_ENDIAN
+#elif defined(__x86_64__)
 #define ON_64BIT_RUNTIME
 #else
 #define ON_32BIT_RUNTIME