1 files changed, 3 insertions, 0 deletions
diff --git a/gl/u64.h b/gl/u64.h
index 11946d4510..de6599038a 100644
--- a/gl/u64.h
+++ b/gl/u64.h
@@ -19,6 +19,9 @@
 
 #include <stdint.h>
 
+#ifndef _GL_INLINE_HEADER_BEGIN
+ #error "Please include config.h first."
+#endif
 _GL_INLINE_HEADER_BEGIN
 #ifndef _GL_U64_INLINE
 # define _GL_U64_INLINE _GL_INLINE