diff --git a/diff.h b/diff.h
index 8ba85c5..a70e7c4 100644
--- a/diff.h
+++ b/diff.h
@@ -283,7 +283,7 @@ struct diff_options {
 	struct diff_flags flags;
 
 	/* diff-filter bits */
-	unsigned int filter;
+	unsigned int filter, filter_not;
 
 	int use_color;