diff --git a/gcc/testsuite/gcc.dg/memchr-3.c b/gcc/testsuite/gcc.dg/memchr-3.c
index c38d9cf3349c2836428186b3af6ead440164c142..af1b26ef3aee538ecaa864f25b9a89a639b42d23 100644
--- a/gcc/testsuite/gcc.dg/memchr-3.c
+++ b/gcc/testsuite/gcc.dg/memchr-3.c
@@ -6,7 +6,7 @@
 typedef __INT8_TYPE__  int8_t;
 typedef __INT32_TYPE__ int32_t;
 
-extern void* memchr (const void*, int, long);
+extern void* memchr (const void*, int, long); /* { dg-warning "-Wbuiltin-declaration-mismatch" { target llp64 } } */
 
 struct SX
 {