diff --git a/dtool/src/dtoolbase/dtoolbase.h b/dtool/src/dtoolbase/dtoolbase.h
index 3f8e07f998..4e7b73ba9a 100644
--- a/dtool/src/dtoolbase/dtoolbase.h
+++ b/dtool/src/dtoolbase/dtoolbase.h
@@ -123,7 +123,7 @@
 
 // This is a workaround for a glibc bug that is triggered by clang when
 // compiling with -ffast-math.
-#ifdef __clang__
+#if defined(__clang__) && defined(__GLIBC__)
 #include <sys/cdefs.h>
 #ifndef __extern_always_inline
 #define __extern_always_inline extern __always_inline