diff --git a/modfile/rule_test.go b/modfile/rule_test.go
index 2ae6b41..1380f16 100644
--- a/modfile/rule_test.go
+++ b/modfile/rule_test.go
@@ -35,6 +35,12 @@ var addParseExtTests = []struct {
 		".spx",
 		"",
 	},
+	{
+		"yap ok",
+		"_yap.gox",
+		"_yap.gox",
+		"",
+	},
 	{
 		"not a ext",
 		"gmx",