diff --git a/conn.go b/conn.go
index f8016220..1693d159 100644
--- a/conn.go
+++ b/conn.go
@@ -707,7 +707,7 @@ func (old ConnConfig) Merge(other ConnConfig) ConnConfig {
 		cc.Dial = other.Dial
 	}
 
-	cc.PreferSimpleProtocol = other.PreferSimpleProtocol
+	cc.PreferSimpleProtocol = old.PreferSimpleProtocol || other.PreferSimpleProtocol
 
 	cc.RuntimeParams = make(map[string]string)
 	for k, v := range old.RuntimeParams {