diff --git a/progs/demos/ray.c b/progs/demos/ray.c
index 2173b54fd4d..fbee960053c 100644
--- a/progs/demos/ray.c
+++ b/progs/demos/ray.c
@@ -8,6 +8,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <math.h>
 
 #ifdef WIN32