diff --git a/contrib/libtests/pngvalid.c b/contrib/libtests/pngvalid.c
index d800110c7..9a2da6a02 100644
--- a/contrib/libtests/pngvalid.c
+++ b/contrib/libtests/pngvalid.c
@@ -22,6 +22,7 @@
 #define _ISOC99_SOURCE 1 /* For floating point */
 #define _GNU_SOURCE 1 /* For the floating point exception extension */
 #define _BSD_SOURCE 1 /* For the floating point exception extension */
+#define _DEFAULT_SOURCE 1 /* For the floating point exception extension */
 
 #include <signal.h>
 #include <stdio.h>