diff --git a/vlib/json/json_primitives.v b/vlib/json/json_primitives.v
index eab1f0a185..517d2583c0 100644
--- a/vlib/json/json_primitives.v
+++ b/vlib/json/json_primitives.v
@@ -12,7 +12,7 @@ struct C.cJSON {
 	valuestring byteptr
 }
 
-pub fn decode() ?voidptr {
+pub fn decode(typ voidptr, s string) ?voidptr {
 	// compiler implementation
 	return 0
 }
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 4c7c7bba41..c4df4dd01e 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -607,12 +607,10 @@ pub fn (mut c Checker) call_method(call_expr mut ast.CallExpr) table.Type {
 			mut scope := c.file.scope.innermost(call_expr.pos.pos)
 			scope.update_var_type('it', array_info.elem_type)
 		}
-
 		mut arg_type := left_type
 		for arg in call_expr.args {
 			arg_type = c.expr(arg.expr)
 		}
-
 		call_expr.return_type = left_type
 		call_expr.receiver_type = left_type
 		if method_name == 'map' && call_expr.args.len == 1 {
@@ -687,17 +685,13 @@ pub fn (mut c Checker) call_method(call_expr mut ast.CallExpr) table.Type {
 		return table.string_type
 	}
 	// call struct field fn type
-	// TODO: can we use SelectorExpr for all? this dosent really belong here
+	// TODO: can we use SelectorExpr for all?
 	if field := c.table.struct_find_field(left_type_sym, method_name) {
 		field_type_sym := c.table.get_type_symbol(field.typ)
 		if field_type_sym.kind == .function {
 			call_expr.is_method = false
 			info := field_type_sym.info as table.FnType
 			call_expr.return_type = info.func.return_type
-			// TODO: check args (do it once for all of the above)
-			for i, arg in call_expr.args {
-				arg_typ := c.expr(arg.expr)
-			}
 			return info.func.return_type
 		}
 	}
@@ -722,6 +716,13 @@ pub fn (mut c Checker) call_fn(call_expr mut ast.CallExpr) table.Type {
 	// }
 	if fn_name == 'json.encode' {
 	}
+	if fn_name == 'json.decode' {
+		ident := call_expr.args[0].expr as ast.Ident
+		// sym := c.table.find_type(ident.name)
+		idx := c.table.find_type_idx(ident.name)
+		println('js.decode t=$ident.name')
+		return table.Type(idx)
+	}
 	// look for function in format `mod.fn` or `fn` (main/builtin)
 	mut f := table.Fn{}
 	mut found := false
@@ -1720,6 +1721,10 @@ pub fn (mut c Checker) ident(ident mut ast.Ident) table.Type {
 	if ident.is_c {
 		return table.int_type
 	}
+	if c.table.known_type(ident.name) {
+		// e.g. `User`  in `json.decode(User, '...')`
+		return table.void_type
+	}
 	if ident.name != '_' {
 		c.error('undefined: `$ident.name`', ident.pos)
 	}
diff --git a/vlib/v/gen/json.v b/vlib/v/gen/json.v
index eab7ccdbfb..6e19efcafc 100644
--- a/vlib/v/gen/json.v
+++ b/vlib/v/gen/json.v
@@ -25,54 +25,25 @@ fn (mut g Gen) gen_json_for_type(typ table.Type) {
 	if sym.name in ['int', 'string', 'bool'] {
 		return
 	}
-	// println('gen_json_for_type( $typ.name )')
-	// Register decoder fn
-	/*
-	mut dec_fn := Fn{
-		mod: p.mod
-		typ: 'Option_$typ.name'
-		name: js_dec_name(t)
-	}
-	if p.table.known_fn(dec_fn.name) {
-		// Already registered? Skip.
-		return
-	}
-
+	// println('gen_json_for_type($typ.name)')
 	// decode_TYPE funcs receive an actual cJSON* object to decode
 	// cJSON_Parse(str) call is added by the compiler
-	arg := Var{
-		typ: 'cJSON*'
-	}
-	dec_fn.args << arg
-	p.table.register_fn(dec_fn)
-	// Register encoder fn
-	mut enc_fn := Fn{
-		mod: p.mod
-		typ: 'cJSON*'
-		name: js_enc_name(t)
-	}
-	// encode_TYPE funcs receive an object to encode
-	enc_arg := Var{
-		typ: t
-	}
-	enc_fn.args << enc_arg
-	p.table.register_fn(enc_fn)
 	// Code gen decoder
-	dec += '
-//$t $dec_fn.name (cJSON* root) {
-Option ${dec_fn.name}(cJSON* root, $t* res) {
-//  $t res;
+	dec_fn_name := js_dec_name(sym.name)
+	dec.writeln('
+Option ${dec_fn_name}(cJSON* root, $styp* res) {
+//  $styp res;
   if (!root) {
     const char *error_ptr = cJSON_GetErrorPtr();
     if (error_ptr != NULL)	{
-      fprintf(stderr, "Error in decode() for $t error_ptr=: %%s\\n", error_ptr);
+      fprintf(stderr, "Error in decode() for $styp error_ptr=: %%s\\n", error_ptr);
 //      printf("\\nbad js=%%s\\n", js.str);
       return v_error(tos2(error_ptr));
     }
   }
-'
-	*/
+')
 	// Code gen encoder
+	// encode_TYPE funcs receive an object to encode
 	enc_fn_name := js_enc_name(sym.name)
 	enc.writeln('
 cJSON* ${enc_fn_name}($styp val) {
@@ -111,7 +82,7 @@ cJSON* ${enc_fn_name}($styp val) {
 	// p.cgen.fns << '$dec return opt_ok(res); \n}'
 	dec.writeln('return opt_ok(res, sizeof(*res)); \n}')
 	enc.writeln('\treturn o;\n}')
-	// g.definitions.writeln(dec.str())
+	g.definitions.writeln(dec.str())
 	g.gowrappers.writeln(enc.str())
 }