diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..714991a
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,44 @@
+name: CI
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+jobs:
+  ci:
+    name: Run checks and tests over ${{matrix.otp}} and ${{matrix.os}}
+    runs-on: ${{matrix.os}}
+    container:
+      image: erlang:${{ matrix.otp }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        otp: ["26.0", "25.3", "24.3"]
+        os: ["ubuntu-22.04"]
+        include:
+          - otp: "23.3"
+            os: "ubuntu-20.04"
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install gettext
+        run: sudo apt-get install -y gettext
+
+      - name: Compile
+        run: rebar3 compile
+
+      - name: xref
+        run: rebar3 xref
+
+      - name: Eunit test
+        run: rebar3 eunit
+
+      - name: Generate docs
+        run: rebar3 edoc
+
+      - name: Dialyze
+        run: rebar3 dialyzer
diff --git a/rebar.config b/rebar.config
index 7a5f391..4228243 100644
--- a/rebar.config
+++ b/rebar.config
@@ -1,4 +1,15 @@
 % -*- mode: erlang -*-
 {erl_opts, [debug_info, fail_on_warning]}.
-%% {yrl_opts, [{verbose, true}]}.
-{lib_dirs, [deps]}.
+
+{xref_checks, [
+        undefined_function_calls,
+        undefined_functions,
+        deprecated_functions_calls,
+        deprecated_functions
+]}.
+
+{dialyzer,
+ [
+  {warnings, [unknown]},
+  {plt_apps, all_deps}
+ ]}.
diff --git a/src/gettexter.app.src b/src/gettexter.app.src
index a8f16c1..8f18c64 100644
--- a/src/gettexter.app.src
+++ b/src/gettexter.app.src
@@ -5,7 +5,8 @@
   {registered, []},
   {applications, [
                   kernel,
-                  stdlib
+                  stdlib,
+                  syntax_tools
                  ]},
   {mod, { gettexter_app, []}},
   {env, []},
diff --git a/src/gettexter.erl b/src/gettexter.erl
index a710674..f3c779d 100644
--- a/src/gettexter.erl
+++ b/src/gettexter.erl
@@ -205,7 +205,7 @@ dnpgettext(Domain, Context, Singular, Plural, N, Locale)
     case Translation of
         undefined when N == 1 -> Singular;
         undefined             -> Plural;
-        Translation           -> Translation
+        _ when is_binary(Translation) -> Translation
     end;
 %% string case
 dnpgettext(Domain, MaybeContext, StrSingular, StrPlural, N, Locale)
diff --git a/src/gettexter_mo_parser.erl b/src/gettexter_mo_parser.erl
index 17f85ec..437f7ee 100644
--- a/src/gettexter_mo_parser.erl
+++ b/src/gettexter_mo_parser.erl
@@ -44,11 +44,11 @@
         {bin :: binary(),
          obin :: binary(),
          catalog=[] :: catalog(),
-         bo :: little | big,
-         version :: integer(),
-         msg_cnt :: integer(),
-         orig_tab_offset :: integer(),
-         trans_tab_offset :: integer()}).
+         bo :: little | big | undefined,
+         version :: integer() | undefined,
+         msg_cnt :: integer() | undefined,
+         orig_tab_offset :: integer() | undefined,
+         trans_tab_offset :: integer() | undefined}).
 
 -spec parse_file(file:filename()) -> #st{}.
 parse_file(Name) ->
diff --git a/src/gettexter_plural.erl b/src/gettexter_plural.erl
index e62db28..b93abc6 100644
--- a/src/gettexter_plural.erl
+++ b/src/gettexter_plural.erl
@@ -37,7 +37,7 @@
 -type opts() :: [{runtime_mod, atom()}  %module used for runtime calls 'to_boolean/1' and 'to_integer/1'
                 ].
 -record(plural_rule_compiled, {nplurals :: non_neg_integer(), %result, returned by compile/2
-                               abstract_form :: erl_parse:abstract_form()}).
+                               abstract_form :: erl_parse:abstract_expr()}).
 
 -record(opts, {runtime_mod = ?MODULE}).
 -define(ES, erl_syntax).
@@ -104,7 +104,7 @@ to_erlang_ast({plural_rule, _, Expr}, Opts) ->
 %% You, most probably, shouldn't call this from your programs.
 %% Return value may be interpreted by `erl_eval:expr/2' (see `plural/2').
 %% May be printed as erlang code snippet by `erl_prettypr' (see `to_erlang_code/2').
--spec to_erlang_abstract(plural_rule(), opts()) -> erl_parse:abstract_form().
+-spec to_erlang_abstract(plural_rule(), opts()) -> erl_parse:abstract_expr().
 to_erlang_abstract({plural_rule, _, _}=Rule, Opts) ->
     erl_syntax:revert(to_erlang_ast(Rule, Opts)).
 
diff --git a/src/gettexter_server.erl b/src/gettexter_server.erl
index 7a85be0..be4f1e8 100644
--- a/src/gettexter_server.erl
+++ b/src/gettexter_server.erl
@@ -37,14 +37,14 @@
 start_link() ->
     gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).
 
--spec dpgettext(atom(), binary(), binary(), binary()) -> binary().
+-spec dpgettext(atom(), binary() | undefined, binary(), binary()) -> binary() | undefined.
 dpgettext(Domain, Context, Text, Locale) ->
     case ets:lookup(?TAB, ?MSG_KEY(Domain, Locale, Context, Text)) of
         []                 -> undefined;
         [{_, Translation}] -> Translation
     end.
 
--spec dnpgettext(atom(), binary(), binary(), binary(), binary(), integer()) -> binary().
+-spec dnpgettext(atom(), binary() | undefined, binary(), binary(), integer(), binary()) -> binary() | undefined.
 dnpgettext(Domain, Context, Singular, Plural, N, Locale) ->
     case ets:lookup(?TAB, ?PLURAL_RULE_KEY(Domain, Locale)) of
         []                  -> undefined;
diff --git a/test/gettexter_tests.erl b/test/gettexter_tests.erl
index cf02125..dcce99c 100644
--- a/test/gettexter_tests.erl
+++ b/test/gettexter_tests.erl
@@ -114,14 +114,15 @@ ensure_mo(Domain, Dir, Locale) ->
     case filelib:is_regular(MoFile) of
         false ->
             PoFile = filename:join([Dir, Locale, "LC_MESSAGES", StrDomain ++ ".po"]),
-            Cmd = ["msgfmt ", "--check ", "-o ", MoFile, " ", PoFile],
-            io:format("~s~n~s", [Cmd, os:cmd(Cmd)]);
+            Cmd = unicode:characters_to_list(["msgfmt ", "--check ", "-o ", MoFile, " ", PoFile]),
+            {ok, Cwd} = file:get_cwd(),
+            io:format(user, "At ~s~n~s~n~s", [Cwd, Cmd, os:cmd(Cmd)]);
         _ -> ok
     end.
 
 start_load() ->
     Pid = start(),
-    Dir = "../test/locale",
+    Dir = "test/locale",
     ensure_mo(?GETTEXT_DOMAIN, Dir, <<"se">>),
     ok = gettexter:bindtextdomain(?GETTEXT_DOMAIN, Dir),
     {ok, _} = gettexter:ensure_loaded(?GETTEXT_DOMAIN, lc_messages, <<"se">>),
@@ -129,7 +130,7 @@ start_load() ->
 
 start_load_string() ->
     Pid = start(),
-    Dir = "../test/locale",
+    Dir = "test/locale",
     ensure_mo(?GETTEXT_DOMAIN, Dir, "se"),
     ok = gettexter:bindtextdomain(?GETTEXT_DOMAIN, Dir),
     {ok, _} = gettexter:ensure_loaded(?GETTEXT_DOMAIN, lc_messages, "se"),