diff --git a/dlls/engine/Makefile.pl b/dlls/engine/Makefile.pl
index 920bb626..44d25a44 100755
--- a/dlls/engine/Makefile.pl
+++ b/dlls/engine/Makefile.pl
@@ -73,7 +73,7 @@ if ($OPTIONS{"debug"})
 
 if ($OPTIONS{"amd64"})
 {
-	$cflags .= "-m64 -DSMALL_CELLSIZE=64 $cflags";
+	$cflags .= " -m64 -DSMALL_CELL_SIZE=64 $cflags";
 }
 
 if ($OPTIONS{"debug"})