diff --git a/src/ejabberd_config.erl b/src/ejabberd_config.erl
index eaf513e77..ed52c728b 100644
--- a/src/ejabberd_config.erl
+++ b/src/ejabberd_config.erl
@@ -713,10 +713,16 @@ process_term(Term, State) ->
 
 process_host_term(Term, Host, State, Action) ->
     case Term of
-        {modules, Modules} when Action == set ->
-            set_option({modules, Host}, replace_modules(Modules), State);
-        {modules, Modules} when Action == append ->
-            append_option({modules, Host}, replace_modules(Modules), State);
+        {modules, Modules} ->
+	    Modules1 = try (gen_mod:opt_type(modules))(Modules) of
+			   _ -> replace_modules(Modules)
+		       catch _:_ -> Modules
+		       end,
+	    if Action == set ->
+		    set_option({modules, Host}, Modules1, State);
+	       Action == append ->
+		    append_option({modules, Host}, Modules1, State)
+	    end;
         {host, _} ->
             State;
         {hosts, _} ->
diff --git a/src/gen_mod.erl b/src/gen_mod.erl
index 4d815073c..cec3ddb24 100644
--- a/src/gen_mod.erl
+++ b/src/gen_mod.erl
@@ -937,8 +937,12 @@ opt_type(modules) ->
     fun(Mods) ->
 	    lists:map(
 	      fun({M, A}) when is_atom(M) ->
-		      true = is_opt_list(A),
-		      {M, A}
+		      case is_opt_list(A) of
+			  true -> {M, A};
+			  false ->
+			      ?ERROR_MSG("Malformed configuration format of module ~s", [M]),
+			      erlang:error(badarg)
+		      end
 	      end, Mods)
     end;
 opt_type(_) -> [modules].