diff --git a/tools_common.c b/tools_common.c
index b481579..7cfd066 100644
--- a/tools_common.c
+++ b/tools_common.c
@@ -246,7 +246,7 @@
     int y;
 
     for (y = 0; y < h; ++y) {
-      if (fread(buf, 1, w, file) != w)
+      if (fread(buf, 1, w, file) != (size_t)w)
         return 0;
       buf += stride;
     }