diff --git a/sys/sys/stdatomic.h b/sys/sys/stdatomic.h
--- a/sys/sys/stdatomic.h
+++ b/sys/sys/stdatomic.h
@@ -33,7 +33,8 @@
 #include <sys/cdefs.h>
 #include <sys/_types.h>
 
-#if __has_extension(c_atomic) || __has_extension(cxx_atomic)
+#if (__has_extension(c_atomic) || __has_extension(cxx_atomic)) && \
+    defined(__clang__)
 #define	__CLANG_ATOMICS
 #elif __GNUC_PREREQ__(4, 7)
 #define	__GNUC_ATOMICS