diff --git a/src/sqerl.erl b/src/sqerl.erl
index eaf074d..37cde21 100644
--- a/src/sqerl.erl
+++ b/src/sqerl.erl
@@ -474,12 +474,15 @@ expr2(undefined, _Safe) -> <<"NULL">>;
 expr2(Expr, _Safe) when is_atom(Expr) -> convert(Expr);
 expr2(Expr, Safe) -> expr(Expr, Safe).
 
-param({call, FuncName, []}) ->
-    [convert(FuncName), <<"()">>];
-param({call, FuncName, Params}) ->
-    [convert(FuncName), $(, make_list(Params, fun param/1), $)];
+param({call, _FuncName, _Params} = Call) ->
+    expr(Call, undefined);
 param({Key, Value}) when is_atom(Key) ->
-    [convert(Key), <<" := ">>, encode(Value)];
+    case Value of
+        {call, _FuncName, _Params} = Call ->
+            [convert(Key), <<" := ">>, expr(Call, undefined)];
+        _ ->
+            [convert(Key), <<" := ">>, encode(Value)]
+    end;
 param(Key) when is_atom(Key) ->
     convert(Key);
 param(Value) ->
diff --git a/test/sqerl_tests.erl b/test/sqerl_tests.erl
index 19832ca..167df4b 100644
--- a/test/sqerl_tests.erl
+++ b/test/sqerl_tests.erl
@@ -210,6 +210,9 @@ safe_test_() ->
             {<<"SELECT name FROM search_people(age := 18)">>,
                 ?_safe_test({select,name,{from,{call,search_people,[{age, 18}]}}})
             },
+            {<<"SELECT name FROM search_people(age := 18, area := postal_code(code := 12345))">>,
+                ?_safe_test({select,name,{from,{call,search_people,[{age,18},{area,{call,postal_code,[{code,12345}]}}]}}})
+            },
             {<<"SELECT * FROM foo JOIN bar ON (foo.bar_id = bar.id)">>,
               ?_safe_test({select,'*',{from,{foo,join,bar,{'foo.bar_id','=','bar.id'}}}})
             },