diff --git a/bacnet-stack/ports/win32/stdbool.h b/bacnet-stack/ports/win32/stdbool.h
index b6bd2e90..1ad2d54e 100644
--- a/bacnet-stack/ports/win32/stdbool.h
+++ b/bacnet-stack/ports/win32/stdbool.h
@@ -3,10 +3,13 @@
 
 /* C99 Boolean types for compilers without C99 support */
 /* http://www.opengroup.org/onlinepubs/009695399/basedefs/stdbool.h.html */
-
 #if !defined(__cplusplus)
 
+#if !defined(__GNUC__)
+/* _Bool builtin type is included in GCC */
 typedef enum { _Bool_must_promote_to_int = -1, false = 0, true = 1 } _Bool;
+#endif
+
 #define bool _Bool
 #define true 1
 #define false 0