diff --git a/src/emqx_frame.erl b/src/emqx_frame.erl
index 0722d996d..17daf9809 100644
--- a/src/emqx_frame.erl
+++ b/src/emqx_frame.erl
@@ -80,6 +80,10 @@
 
 -dialyzer({no_match, [serialize_utf8_string/2]}).
 
+-ifdef(TEST).
+-export([parse_variable_byte_integer/1]).
+-endif.
+
 %%--------------------------------------------------------------------
 %% Init Parse State
 %%--------------------------------------------------------------------
diff --git a/test/emqx_frame_SUITE.erl b/test/emqx_frame_SUITE.erl
index 591c75bdc..4b43c8506 100644
--- a/test/emqx_frame_SUITE.erl
+++ b/test/emqx_frame_SUITE.erl
@@ -43,7 +43,9 @@ groups() ->
     [{parse, [parallel],
       [t_parse_cont,
        t_parse_frame_too_large,
-       t_parse_frame_malformed_variable_byte_integer
+       t_parse_frame_malformed_variable_byte_integer,
+       t_parse_frame_variable_byte_integer,
+       t_parse_frame_proxy_protocol %% proxy_protocol_config_disabled packet.
       ]},
      {connect, [parallel],
       [t_serialize_parse_v3_connect,
@@ -142,6 +144,13 @@ t_parse_frame_variable_byte_integer(_) ->
     ?catch_error(malformed_variable_byte_integer,
         emqx_frame:parse_variable_byte_integer(Bin)).
 
+t_parse_frame_proxy_protocol(_) ->
+    BinList = [ <<"PROXY TCP4 ">>, <<"PROXY TCP6 ">>, <<"PROXY UNKNOWN">>
+              , <<"\r\n\r\n\0\r\nQUIT\n">>],
+    [?assertError( proxy_protocol_config_disabled
+                 , emqx_frame:parse(Bin))
+     || Bin <- BinList].
+
 t_serialize_parse_v3_connect(_) ->
     Bin = <<16,37,0,6,77,81,73,115,100,112,3,2,0,60,0,23,109,111,115,
             113,112,117, 98,47,49,48,52,53,49,45,105,77,97,99,46,108,
@@ -555,4 +564,3 @@ parse_to_packet(Bin, Opts) ->
     Packet.
 
 payload(Len) -> iolist_to_binary(lists:duplicate(Len, 1)).
-