diff --git a/configure b/configure
index 28b5a4cfc4..25401dd37d 100755
--- a/configure
+++ b/configure
@@ -3441,7 +3441,9 @@ echores "$_strsep"
 
 echocheck "vsscanf()"
 cat > $TMPC << EOF
+#define _ISOC99_SOURCE
 #include <stdarg.h>
+#include <stdio.h>
 int main(void) { vsscanf(0, 0, 0); return 0; }
 EOF
 _vsscanf=no