diff --git a/mingw-w64-tools/gendef/src/gendef.c b/mingw-w64-tools/gendef/src/gendef.c
index 3ec48a6..f80cec2 100644
--- a/mingw-w64-tools/gendef/src/gendef.c
+++ b/mingw-w64-tools/gendef/src/gendef.c
@@ -248,7 +248,7 @@
   fclose (fp);
   if (!gDta)
     {
-      fprintf (stderr, "*** [%s] unable to allocate %Iu bytes\n" ,fninput,
+      fprintf (stderr, "*** [%s] unable to allocate %lu bytes\n", fninput,
 	       (unsigned long) gDta_size);
       return 0;
     }