diff --git a/jcl/source/vcl/JclGraphUtils.pas b/jcl/source/vcl/JclGraphUtils.pas
index d4aff254bd..9b617bda86 100644
--- a/jcl/source/vcl/JclGraphUtils.pas
+++ b/jcl/source/vcl/JclGraphUtils.pas
@@ -380,7 +380,7 @@ procedure GDIError;
 begin
   ErrorCode := GetLastError;
   if (ErrorCode <> 0) and (FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, nil,
-    ErrorCode, LOCALE_USER_DEFAULT, Buf, SizeOf(Buf), nil) <> 0) then
+    ErrorCode, LOCALE_USER_DEFAULT, Buf, Length(Buf), nil) <> 0) then
     raise EOutOfResources.Create(Buf)
   else
     OutOfResources;