diff --git a/src/common/proc_args.c b/src/common/proc_args.c
index 535fc20c570f81cb7bb64d134396fc73193e25aa..83761103b40061b54148086d14a27a6e75a2b689 100644
--- a/src/common/proc_args.c
+++ b/src/common/proc_args.c
@@ -46,6 +46,10 @@
 #  include <strings.h>
 #endif
 
+#ifndef __USE_ISOC99
+#define __USE_ISOC99
+#endif
+
 #ifdef HAVE_LIMITS_H
 #  include <limits.h>
 #endif