diff --git a/credentials/credentials.go b/credentials/credentials.go
index 0c2b24c0..c1a331e8 100644
--- a/credentials/credentials.go
+++ b/credentials/credentials.go
@@ -51,7 +51,7 @@ import (
 
 var (
 	// alpnProtoStr are the specified application level protocols for gRPC.
-	alpnProtoStr = []string{"h2", "h2-14", "h2-15", "h2-16"}
+	alpnProtoStr = []string{"h2"}
 )
 
 // Credentials defines the common interface all supported credentials must