diff --git a/src/emqx_frame.erl b/src/emqx_frame.erl
index 60d8f52f8..2149833d6 100644
--- a/src/emqx_frame.erl
+++ b/src/emqx_frame.erl
@@ -78,6 +78,10 @@
 
 -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 ee2982611..c51ab8d7f 100644
--- a/test/emqx_frame_SUITE.erl
+++ b/test/emqx_frame_SUITE.erl
@@ -44,7 +44,9 @@ groups() ->
       [t_parse_cont,
        t_parse_frame_too_large,
        t_parse_frame_malformed_variable_byte_integer,
-       t_parse_malformed_utf8_string
+       t_parse_frame_variable_byte_integer,
+       t_parse_malformed_utf8_string,
+       t_parse_frame_proxy_protocol %% proxy_protocol_config_disabled packet.
       ]},
      {connect, [parallel],
       [t_serialize_parse_v3_connect,
@@ -137,6 +139,10 @@ t_parse_frame_malformed_variable_byte_integer(_) ->
     ?catch_error(malformed_variable_byte_integer,
         emqx_frame:parse(MalformedPayload, ParseState)).
 
+t_parse_frame_variable_byte_integer(_) ->
+    Bin = <<2#10010011, 2#10000000, 2#10001000, 2#10011001, 2#10101101, 2#00110010>>,
+    ?catch_error(malformed_variable_byte_integer,
+        emqx_frame:parse_variable_byte_integer(Bin)).
 
 t_parse_malformed_utf8_string(_) ->
     MalformedPacket = <<16,31,0,4,
@@ -155,6 +161,13 @@ t_parse_malformed_utf8_string(_) ->
     ParseState = emqx_frame:initial_parse_state(#{strict_mode => true}),
     ?catch_error(utf8_string_invalid, emqx_frame:parse(MalformedPacket, ParseState)).
 
+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,
@@ -550,4 +563,3 @@ parse_to_packet(Bin, Opts) ->
     Packet.
 
 payload(Len) -> iolist_to_binary(lists:duplicate(Len, 1)).
-