diff --git a/gcc/testsuite/g++.dg/warn/Wsystem-headers1.C b/gcc/testsuite/g++.dg/warn/Wsystem-headers1.C
index ac5c30d3dbc..c927b367243 100644
--- a/gcc/testsuite/g++.dg/warn/Wsystem-headers1.C
+++ b/gcc/testsuite/g++.dg/warn/Wsystem-headers1.C
@@ -1,3 +1,3 @@
 #include <stdlib.h>
 
-extern double atof (const char *);
+extern "C" double atof (const char *);