diff --git a/codecs/gsm/inc/proto.h b/codecs/gsm/inc/proto.h
index 87cf05e8a7..68e1ecf052 100644
--- a/codecs/gsm/inc/proto.h
+++ b/codecs/gsm/inc/proto.h
@@ -9,11 +9,11 @@
 #ifndef	PROTO_H
 #define	PROTO_H
 
-#if __cplusplus
+#ifdef __cplusplus
 #	define	NeedFunctionPrototypes	1
 #endif
 
-#if __STDC__
+#ifdef __STDC__
 #	define	NeedFunctionPrototypes	1
 #endif