diff --git a/src/ra.hrl b/src/ra.hrl
index 14503d48..2d6856f5 100644
--- a/src/ra.hrl
+++ b/src/ra.hrl
@@ -253,6 +253,7 @@
 -define(C_RA_SRV_AER_RECEIVED_FOLLOWER_EMPTY, ?C_RA_LOG_RESERVED + 17).
 -define(C_RA_SRV_TERM_AND_VOTED_FOR_UPDATES, ?C_RA_LOG_RESERVED + 18).
 -define(C_RA_SRV_LOCAL_QUERIES, ?C_RA_LOG_RESERVED + 19).
+-define(C_RA_SRV_INVALID_REPLY_MODE_COMMANDS, ?C_RA_LOG_RESERVED + 20).
 
 
 -define(RA_SRV_COUNTER_FIELDS,
@@ -294,7 +295,9 @@
          {term_and_voted_for_updates, ?C_RA_SRV_TERM_AND_VOTED_FOR_UPDATES, counter,
           "Total number of updates of term and voted for"},
          {local_queries, ?C_RA_SRV_LOCAL_QUERIES, counter,
-          "Total number of local queries"}
+          "Total number of local queries"},
+         {invalid_reply_mode_commands, ?C_RA_SRV_INVALID_REPLY_MODE_COMMANDS, counter,
+          "Total number of commands received with an invalid reply-mode"}
          ]).
 
 -define(RA_COUNTER_FIELDS, ?RA_LOG_COUNTER_FIELDS ++ ?RA_SRV_COUNTER_FIELDS).
diff --git a/src/ra_server_proc.erl b/src/ra_server_proc.erl
index adec4611..72de91d1 100644
--- a/src/ra_server_proc.erl
+++ b/src/ra_server_proc.erl
@@ -353,7 +353,7 @@ leader(EventType, {local_call, Msg}, State) ->
 leader(EventType, {leader_cast, Msg}, State) ->
     leader(EventType, Msg, State);
 leader(EventType, {command, normal, {CmdType, Data, ReplyMode}},
-       #state{server_state = ServerState0} = State0) ->
+       #state{conf = Conf, server_state = ServerState0} = State0) ->
     case validate_reply_mode(ReplyMode) of
         ok ->
             %% normal priority commands are written immediately
@@ -365,6 +365,7 @@ leader(EventType, {command, normal, {CmdType, Data, ReplyMode}},
                                 State0#state{server_state = ServerState}),
             {keep_state, State, Actions};
         Error ->
+            ok = incr_counter(Conf, ?C_RA_SRV_INVALID_REPLY_MODE_COMMANDS, 1),
             case EventType of
                 {call, From} ->
                     {keep_state, State0, [{reply, From, Error}]};
@@ -373,7 +374,7 @@ leader(EventType, {command, normal, {CmdType, Data, ReplyMode}},
             end
     end;
 leader(EventType, {command, low, {CmdType, Data, ReplyMode}},
-       #state{delayed_commands = Delayed} = State0) ->
+       #state{conf = Conf, delayed_commands = Delayed} = State0) ->
     case validate_reply_mode(ReplyMode) of
         ok ->
             %% cache the low priority command until the flush_commands message
@@ -395,6 +396,7 @@ leader(EventType, {command, low, {CmdType, Data, ReplyMode}},
             State = State0#state{delayed_commands = queue:in(Cmd, Delayed)},
             {keep_state, State, []};
         Error ->
+            ok = incr_counter(Conf, ?C_RA_SRV_INVALID_REPLY_MODE_COMMANDS, 1),
             case EventType of
                 {call, From} ->
                     {keep_state, State0, [{reply, From, Error}]};