diff --git a/include/tradstdc.h b/include/tradstdc.h
index 02f4c4a57..afbafe584 100644
--- a/include/tradstdc.h
+++ b/include/tradstdc.h
@@ -472,9 +472,11 @@ inline char *rindex(const char *s, int c) __attribute__ ((unavailable));
 #endif
 #endif
 #if defined(__clang__)
+#if __clang_major__ >= 7
 inline char *index(const char *s, int c) __attribute__ ((unavailable));
 inline char *rindex(const char *s, int c) __attribute__ ((unavailable));
 #endif
+#endif
 
 
 #endif /* TRADSTDC_H */