diff --git a/schema_parse.go b/schema_parse.go
index 09040856..4f5622ae 100644
--- a/schema_parse.go
+++ b/schema_parse.go
@@ -565,6 +565,7 @@ func derefSchema(schema Schema) Schema {
 		}
 
 		if _, haveSeen := seen[ref.Schema().FullName()]; !haveSeen {
+			seen[ref.Schema().FullName()] = struct{}{}
 			return ref.Schema()
 		}
 		return schema