diff --git a/tumble_png.c b/tumble_png.c
index 78ad719..04ec93f 100644
--- a/tumble_png.c
+++ b/tumble_png.c
@@ -27,6 +27,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
 #include <strings.h>  /* strcasecmp() is a BSDism */