diff --git a/arch/x86/include/libucontext/bits.h b/arch/x86/include/libucontext/bits.h
index 9fd1bf0..07a9c59 100644
--- a/arch/x86/include/libucontext/bits.h
+++ b/arch/x86/include/libucontext/bits.h
@@ -1,19 +1,19 @@
 #ifndef LIBUCONTEXT_BITS_H
 #define LIBUCONTEXT_BITS_H
 
-#define REG_GS		(0)
-#define REG_FS		(1)
-#define REG_ES		(2)
-#define REG_DS		(3)
-#define REG_EDI		(4)
-#define REG_ESI		(5)
-#define REG_EBP		(6)
-#define REG_ESP		(7)
-#define REG_EBX		(8)
-#define REG_EDX		(9)
-#define REG_ECX		(10)
-#define REG_EAX		(11)
-#define REG_EIP		(14)
+#define LIBUCONTEXT_REG_GS		(0)
+#define LIBUCONTEXT_REG_FS		(1)
+#define LIBUCONTEXT_REG_ES		(2)
+#define LIBUCONTEXT_REG_DS		(3)
+#define LIBUCONTEXT_REG_EDI		(4)
+#define LIBUCONTEXT_REG_ESI		(5)
+#define LIBUCONTEXT_REG_EBP		(6)
+#define LIBUCONTEXT_REG_ESP		(7)
+#define LIBUCONTEXT_REG_EBX		(8)
+#define LIBUCONTEXT_REG_EDX		(9)
+#define LIBUCONTEXT_REG_ECX		(10)
+#define LIBUCONTEXT_REG_EAX		(11)
+#define LIBUCONTEXT_REG_EIP		(14)
 
 typedef int libucontext_greg_t, libucontext_gregset_t[19];
 
@@ -47,4 +47,3 @@ typedef struct libucontext_ucontext {
 } libucontext_ucontext_t;
 
 #endif
-
diff --git a/arch/x86_64/include/libucontext/bits.h b/arch/x86_64/include/libucontext/bits.h
index 87de408..b8f1deb 100644
--- a/arch/x86_64/include/libucontext/bits.h
+++ b/arch/x86_64/include/libucontext/bits.h
@@ -3,29 +3,29 @@
 #ifndef LIBUCONTEXT_BITS_H
 #define LIBUCONTEXT_BITS_H
 
-#define REG_R8		(0)
-#define REG_R9 		(1)
-#define REG_R10 	(2)
-#define REG_R11		(3)
-#define REG_R12		(4)
-#define REG_R13		(5)
-#define REG_R14		(6)
-#define REG_R15		(7)
-#define REG_RDI		(8)
-#define REG_RSI		(9)
-#define REG_RBP		(10)
-#define REG_RBX		(11)
-#define REG_RDX		(12)
-#define REG_RAX		(13)
-#define REG_RCX		(14)
-#define REG_RSP		(15)
-#define REG_RIP		(16)
-#define REG_EFL		(17)
-#define REG_CSGSFS	(18)
-#define REG_ERR		(19)
-#define REG_TRAPNO	(20)
-#define REG_OLDMASK	(21)
-#define REG_CR2		(22)
+#define LIBUCONTEXT_REG_R8		(0)
+#define LIBUCONTEXT_REG_R9 		(1)
+#define LIBUCONTEXT_REG_R10 	(2)
+#define LIBUCONTEXT_REG_R11		(3)
+#define LIBUCONTEXT_REG_R12		(4)
+#define LIBUCONTEXT_REG_R13		(5)
+#define LIBUCONTEXT_REG_R14		(6)
+#define LIBUCONTEXT_REG_R15		(7)
+#define LIBUCONTEXT_REG_RDI		(8)
+#define LIBUCONTEXT_REG_RSI		(9)
+#define LIBUCONTEXT_REG_RBP		(10)
+#define LIBUCONTEXT_REG_RBX		(11)
+#define LIBUCONTEXT_REG_RDX		(12)
+#define LIBUCONTEXT_REG_RAX		(13)
+#define LIBUCONTEXT_REG_RCX		(14)
+#define LIBUCONTEXT_REG_RSP		(15)
+#define LIBUCONTEXT_REG_RIP		(16)
+#define LIBUCONTEXT_REG_EFL		(17)
+#define LIBUCONTEXT_REG_CSGSFS	(18)
+#define LIBUCONTEXT_REG_ERR		(19)
+#define LIBUCONTEXT_REG_TRAPNO	(20)
+#define LIBUCONTEXT_REG_OLDMASK	(21)
+#define LIBUCONTEXT_REG_CR2		(22)
 
 typedef long long libucontext_greg_t, libucontext_gregset_t[23];
 
diff --git a/test_libucontext.c b/test_libucontext.c
index 3e40f3a..33bad1a 100644
--- a/test_libucontext.c
+++ b/test_libucontext.c
@@ -9,6 +9,16 @@
 #include <string.h>
 #include <libucontext/libucontext.h>
 
+/* Verify libucontext's public headers do not shadow libc's REG_* enum
+ * members from <sys/ucontext.h>.  Including it after libucontext.h is
+ * the order that used to produce a hard syntax error on x86/x86_64 in
+ * freestanding mode. */
+#if defined(__has_include)
+# if __has_include(<sys/ucontext.h>)
+#  include <sys/ucontext.h>
+# endif
+#endif
+
 #define handle_error(msg) \
            do { perror(msg); exit(EXIT_FAILURE); } while (0)