diff --git a/MagickCore/string_.h b/MagickCore/string_.h
index efb8eef..9217187 100644
--- a/MagickCore/string_.h
+++ b/MagickCore/string_.h
@@ -79,7 +79,7 @@
 
 extern MagickExport ssize_t
   FormatMagickSize(const MagickSizeType,const MagickBooleanType,const char *,
-    char *),
+    const size_t,char *),
   FormatMagickTime(const time_t,const size_t,char *);
 
 extern MagickExport StringInfo