diff --git a/image/png_image.cpp b/image/png_image.cpp
index 37875fc..1531d6f 100644
--- a/image/png_image.cpp
+++ b/image/png_image.cpp
@@ -4,6 +4,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include <png.h>
 #include "png_image.h"