diff --git a/Mac/Modules/macosmodule.c b/Mac/Modules/macosmodule.c
index 7dcc497..c1bab50 100644
--- a/Mac/Modules/macosmodule.c
+++ b/Mac/Modules/macosmodule.c
@@ -185,7 +185,7 @@
 	bgi = bgy = -2;	
 	if (!PyArg_ParseTuple(args, "ll|ll", &fgi, &fgy, &bgi, &bgy))
 		return NULL;
-	if ( bgi == -2 ) {
+	if ( bgi == -2 || bgy == -2 ) {
 		bgi = fgi;
 		bgy = fgy;
 	}