diff --git a/big_tests/tests/offline_SUITE.erl b/big_tests/tests/offline_SUITE.erl
index a214bcd3e9c..294877cdcbc 100644
--- a/big_tests/tests/offline_SUITE.erl
+++ b/big_tests/tests/offline_SUITE.erl
@@ -109,7 +109,9 @@ config_with_groupchat_modules(Backend) ->
 chatmarkers_modules() ->
     [{mod_smart_markers, config_parser_helper:default_mod_config(mod_smart_markers)},
      {mod_offline, config_with_groupchat_modules(rdbms)},
-     {mod_offline_chatmarkers, [{store_groupchat_messages, true}]},
+     {mod_offline_chatmarkers,
+      mod_config(mod_offline_chatmarkers,
+                 #{store_groupchat_messages => true})},
      {mod_muc_light, mod_config(mod_muc_light, #{backend => rdbms})}].
 
 end_per_group(Group, C) when Group =:= chatmarkers;
diff --git a/src/config/mongoose_config_parser_toml.erl b/src/config/mongoose_config_parser_toml.erl
index 49c3a90d34c..dbf61f7a407 100644
--- a/src/config/mongoose_config_parser_toml.erl
+++ b/src/config/mongoose_config_parser_toml.erl
@@ -110,7 +110,7 @@ get_spec_for_key(Key, Items) ->
         false ->
             case maps:find(default, Items) of
                 {ok, Spec} -> Spec;
-                error -> error(#{what => unexpected_key, key => Key})
+                error -> error(#{what => unexpected_key, key => Key, items => Items})
             end
     end.
 
diff --git a/src/config/mongoose_config_spec.erl b/src/config/mongoose_config_spec.erl
index 6f7794002a9..6a90e729f6b 100644
--- a/src/config/mongoose_config_spec.erl
+++ b/src/config/mongoose_config_spec.erl
@@ -821,6 +821,7 @@ configurable_modules() ->
      mod_muc_light,
      mod_muc_log,
      mod_offline,
+     mod_offline_chatmarkers,
      mod_ping,
      mod_privacy,
      mod_private,
diff --git a/src/offline/mod_offline_chatmarkers.erl b/src/offline/mod_offline_chatmarkers.erl
index 3f866b6fd40..67b5685d4f3 100644
--- a/src/offline/mod_offline_chatmarkers.erl
+++ b/src/offline/mod_offline_chatmarkers.erl
@@ -40,6 +40,7 @@
 -export([stop/1]).
 -export([deps/2]).
 -export([supported_features/0]).
+-export([config_spec/0]).
 
 %% Hook handlers
 -export([inspect_packet/4,
@@ -52,6 +53,7 @@
 
 -include("jlib.hrl").
 -include_lib("exml/include/exml.hrl").
+-include("mongoose_config_spec.hrl").
 
 %% gen_mod callbacks
 %% ------------------------------------------------------------------
@@ -61,15 +63,17 @@ supported_features() ->
     [dynamic_domains].
 
 -spec deps(mongooseim:host_type(), gen_mod:module_opts()) -> gen_mod_deps:deps().
-deps(_,_)->
+deps(_, _)->
     [].  %% TODO: this need to be marked as required-to-be-configured
     % [{mod_smart_markers, [], hard}].
 
+-spec start(mongooseim:host_type(), gen_mod:module_opts()) -> ok.
 start(HostType, Opts) ->
-    mod_offline_chatmarkers_backend:init(HostType, add_default_backend(Opts)),
+    mod_offline_chatmarkers_backend:init(HostType, Opts),
     ejabberd_hooks:add(hooks(HostType)),
     ok.
 
+-spec stop(mongooseim:host_type()) -> ok.
 stop(HostType) ->
     ejabberd_hooks:delete(hooks(HostType)),
     ok.
@@ -80,7 +84,7 @@ hooks(HostType) ->
         {resend_offline_messages_hook, HostType, ?MODULE, pop_offline_messages, 60},
         {remove_user, HostType, ?MODULE, remove_user, 50}
     ],
-    case gen_mod:get_module_opt(HostType, ?MODULE, store_groupchat_messages, false) of
+    case gen_mod:get_module_opt(HostType, ?MODULE, store_groupchat_messages) of
         true ->
             GroupChatHook = {offline_groupchat_message_hook,
                              HostType, ?MODULE, inspect_packet, 40},
@@ -88,9 +92,22 @@ hooks(HostType) ->
         _ -> DefaultHooks
     end.
 
+-spec config_spec() -> mongoose_config_spec:config_section().
+config_spec() ->
+    #section{
+        items = #{<<"backend">> => #option{type = atom,
+                                           validate = {module, ?MODULE}},
+                  <<"store_groupchat_messages">> => #option{type = boolean}
+                 },
+        defaults = #{<<"store_groupchat_messages">> => false,
+                     <<"backend">> => rdbms
+                    },
+        format_items = map
+        }.
+
 remove_user(Acc, User, Server) ->
     HostType = mongoose_acc:host_type(Acc),
-    mod_offline_chatmarkers_backend:remove_user(HostType, jid:make(User, Server, <<"">>)),
+    mod_offline_chatmarkers_backend:remove_user(HostType, jid:make(User, Server, <<>>)),
     Acc.
 
 pop_offline_messages(Acc, JID) ->
@@ -177,11 +194,3 @@ thread(undefined) -> [];
 thread(Thread) ->
     [#xmlel{name     = <<"thread">>, attrs = [],
             children = [#xmlcdata{content = Thread}]}].
-
-add_default_backend(Opts) ->
-    case lists:keyfind(backend, 2, Opts) of
-        false ->
-            [{backend, rdbms} | Opts];
-        _ ->
-            Opts
-    end.
diff --git a/test/common/config_parser_helper.erl b/test/common/config_parser_helper.erl
index af9824f9831..6dc1c618d09 100644
--- a/test/common/config_parser_helper.erl
+++ b/test/common/config_parser_helper.erl
@@ -957,6 +957,9 @@ default_mod_config(mod_offline) ->
     #{backend => mnesia,
       access_max_user_messages => max_user_offline_messages,
       store_groupchat_messages => false};
+default_mod_config(mod_offline_chatmarkers) ->
+    #{backend => rdbms,
+      store_groupchat_messages => false};
 default_mod_config(mod_privacy) ->
     #{backend => mnesia};
 default_mod_config(mod_private) ->
diff --git a/test/config_parser_SUITE.erl b/test/config_parser_SUITE.erl
index cffca714463..0fecaad5d27 100644
--- a/test/config_parser_SUITE.erl
+++ b/test/config_parser_SUITE.erl
@@ -233,6 +233,7 @@ groups() ->
                             mod_muc_light,
                             mod_muc_light_config_schema,
                             mod_offline,
+                            mod_offline_chatmarkers,
                             mod_ping,
                             mod_privacy,
                             mod_private,
@@ -2534,6 +2535,17 @@ mod_offline(_Config) ->
     ?errh(T(#{<<"riak">> => #{<<"bucket_type">> => 1}})),
     ?errh(T(#{<<"riak">> => #{<<"bucket">> => <<"leaky">>}})).
 
+mod_offline_chatmarkers(_Config) ->
+    check_module_defaults(mod_offline_chatmarkers),
+    T = fun(Opts) -> #{<<"modules">> => #{<<"mod_offline_chatmarkers">> => Opts}} end,
+    P = [modules, mod_offline_chatmarkers],
+    ?cfgh(P ++ [backend], rdbms,
+          T(#{<<"backend">> => <<"rdbms">>})),
+    ?cfgh(P ++ [store_groupchat_messages], true,
+          T(#{<<"store_groupchat_messages">> => true})),
+    ?errh(T(#{<<"store_groupchat_messages">> => 1})),
+    ?errh(T(#{<<"backend">> => <<"riak_is_the_best">>})).
+
 mod_ping(_Config) ->
     T = fun(Opts) -> #{<<"modules">> => #{<<"mod_ping">> => Opts}} end,
     P = [modules, mod_ping],
@@ -3382,10 +3394,10 @@ handle_module_options(V1, V2) ->
     ?eq(V1, V2).
 
 %% Generic assertions, use the 'F' handler for any custom cases
-compare_unordered_lists(L1, L2) ->
+compare_unordered_lists(L1, L2) when is_list(L1), is_list(L2) ->
     compare_unordered_lists(L1, L2, fun(V1, V2) -> ?eq(V1, V2) end).
 
-compare_unordered_lists(L1, L2, F) ->
+compare_unordered_lists(L1, L2, F) when is_list(L1), is_list(L2) ->
     SL1 = lists:sort(L1),
     SL2 = lists:sort(L2),
     compare_ordered_lists(SL1, SL2, F).