diff --git a/src/internal.h b/src/internal.h
index 09c19eae6a93e38a3bfbd74d43ba9a9f1f83a9c9..5ca1fa36eea0adb30e4a705cdc688c47a7560c8d 100644
--- a/src/internal.h
+++ b/src/internal.h
@@ -100,6 +100,8 @@
 #ifndef ATTRIBUTE_SENTINEL
 #if __GNUC_PREREQ (4, 0)
 #define ATTRIBUTE_SENTINEL __attribute__((__sentinel__))
+#else
+#define ATTRIBUTE_SENTINEL
 #endif
 #endif