diff -rupN a/lib/gif_lib.h b/lib/gif_lib.h
--- a/lib/gif_lib.h	2013-01-06 07:29:57.000000000 +0100
+++ b/lib/gif_lib.h	2013-07-30 10:52:47.611034000 +0200
@@ -19,6 +19,7 @@ extern "C" {
 #define GIF_OK      1
 
 #include <stdbool.h>
+#include <stddef.h>
 
 #define GIF_STAMP "GIFVER"          /* First chars in file - GIF stamp.  */
 #define GIF_STAMP_LEN sizeof(GIF_STAMP) - 1