diff --git a/src/rwpng.c b/src/rwpng.c
index aaa21fc..11d698f 100644
--- a/src/rwpng.c
+++ b/src/rwpng.c
@@ -30,10 +30,12 @@
   ---------------------------------------------------------------------------*/
 
 #include <stdio.h>
+#include <string.h>
 #include <stdlib.h>
 
 #include "png.h"        /* libpng header; includes zlib.h */
 #include "rwpng.h"      /* typedefs, common macros, public prototypes */
+#include <zlib.h>
 
 /* future versions of libpng will provide this macro: */
 /* GRR NOTUSED */