diff --git a/include/QF/qtypes.h b/include/QF/qtypes.h
index a44eceadc..e4fa1a6b2 100644
--- a/include/QF/qtypes.h
+++ b/include/QF/qtypes.h
@@ -46,7 +46,13 @@ typedef unsigned char byte;
 // KJB Undefined true and false defined in SciTech's DEBUG.H header
 #undef true
 #undef false
+# ifdef __bool_true_false_are_defined
+typedef enum    {q_false, q_true} qboolean
+#define true q_true;
+#define false q_false;
+# else
 typedef	enum	{false, true} qboolean;
+# endif
 #endif
 
 // From mathlib...