diff --git a/vlib/json/json_primitives.v b/vlib/json/json_primitives.v
index 517d2583c0..a0a7af47e7 100644
--- a/vlib/json/json_primitives.v
+++ b/vlib/json/json_primitives.v
@@ -6,6 +6,7 @@ module json
 #flag -I @VROOT/thirdparty/cJSON
 #flag @VROOT/thirdparty/cJSON/cJSON.o
 #include "cJSON.h"
+#define js_get(object, key) cJSON_GetObjectItemCaseSensitive((object), (key))
 struct C.cJSON {
 	valueint    int
 	valuedouble f32
@@ -22,84 +23,84 @@ pub fn encode(x voidptr) string {
 	return ''
 }
 
-fn jsdecode_int(root &C.cJSON) int {
+fn decode_int(root &C.cJSON) int {
 	if isnil(root) {
 		return 0
 	}
 	return root.valueint
 }
 
-fn jsdecode_i8(root &C.cJSON) i8 {
+fn decode_i8(root &C.cJSON) i8 {
 	if isnil(root) {
 		return i8(0)
 	}
 	return i8(root.valueint)
 }
 
-fn jsdecode_i16(root &C.cJSON) i16 {
+fn decode_i16(root &C.cJSON) i16 {
 	if isnil(root) {
 		return i16(0)
 	}
 	return i16(root.valueint)
 }
 
-fn jsdecode_i64(root &C.cJSON) i64 {
+fn decode_i64(root &C.cJSON) i64 {
 	if isnil(root) {
 		return i64(0)
 	}
 	return i64(root.valuedouble) // i64 is double in C
 }
 
-fn jsdecode_byte(root &C.cJSON) byte {
+fn decode_byte(root &C.cJSON) byte {
 	if isnil(root) {
 		return byte(0)
 	}
 	return byte(root.valueint)
 }
 
-fn jsdecode_u16(root &C.cJSON) u16 {
+fn decode_u16(root &C.cJSON) u16 {
 	if isnil(root) {
 		return u16(0)
 	}
 	return u16(root.valueint)
 }
 
-fn jsdecode_u32(root &C.cJSON) u32 {
+fn decode_u32(root &C.cJSON) u32 {
 	if isnil(root) {
 		return u32(0)
 	}
 	return u32(root.valueint)
 }
 
-fn jsdecode_u64(root &C.cJSON) u64 {
+fn decode_u64(root &C.cJSON) u64 {
 	if isnil(root) {
 		return u64(0)
 	}
 	return u64(root.valueint)
 }
 
-fn jsdecode_f32(root &C.cJSON) f32 {
+fn decode_f32(root &C.cJSON) f32 {
 	if isnil(root) {
 		return f32(0)
 	}
 	return root.valuedouble
 }
 
-fn jsdecode_f64(root &C.cJSON) f64 {
+fn decode_f64(root &C.cJSON) f64 {
 	if isnil(root) {
 		return f64(0)
 	}
 	return f64(root.valuedouble)
 }
 
-fn jsdecode_string(root &C.cJSON) string {
+fn decode_string(root &C.cJSON) string {
 	if isnil(root) {
 		return ''
 	}
 	if isnil(root.valuestring) {
 		return ''
 	}
-	// println('jsdecode string valuestring="$root.valuestring"')
+	// println('decode string valuestring="$root.valuestring"')
 	// return tos(root.valuestring, _strlen(root.valuestring))
 	return tos_clone(root.valuestring) // , _strlen(root.valuestring))
 }
@@ -122,7 +123,7 @@ fn C.cJSON_Parse() &C.cJSON
 fn C.cJSON_PrintUnformatted() byteptr
 
 
-fn jsdecode_bool(root &C.cJSON) bool {
+fn decode_bool(root &C.cJSON) bool {
 	if isnil(root) {
 		return false
 	}
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index ea810d3c9c..39b81ae5af 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -721,13 +721,14 @@ pub fn (mut c Checker) call_fn(call_expr mut ast.CallExpr) table.Type {
 	// println(fn_name)
 	// }
 	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)
+	} else if fn_name == 'json.decode' {
+		expr := call_expr.args[0].expr
+		if !(expr is ast.Type) {
+			c.error('json.decode: first argument needs to be a type', call_expr.pos)
+			return table.void_type
+		}
+		typ := expr as ast.Type
+		return typ.typ.set_flag(.optional)
 	}
 	// look for function in format `mod.fn` or `fn` (main/builtin)
 	mut f := table.Fn{}
diff --git a/vlib/v/gen/fn.v b/vlib/v/gen/fn.v
index 71f498cfb4..e6abdc3122 100644
--- a/vlib/v/gen/fn.v
+++ b/vlib/v/gen/fn.v
@@ -383,12 +383,22 @@ fn (mut g Gen) fn_call(node ast.CallExpr) {
 	mut name := node.name
 	is_print := name == 'println' || name == 'print'
 	print_method := if name == 'println' { 'println' } else { 'print' }
-	g.is_json_fn = name == 'json.encode'
+	is_json_encode := name == 'json.encode'
+	is_json_decode := name == 'json.decode'
+	g.is_json_fn = is_json_encode || is_json_decode
 	mut json_type_str := ''
 	if g.is_json_fn {
-		g.write('json__json_print(')
-		g.gen_json_for_type(node.args[0].typ)
-		json_type_str = g.table.get_type_symbol(node.args[0].typ).name
+		if name == 'json.encode' {
+			g.write('json__json_print(')
+			g.gen_json_for_type(node.args[0].typ)
+			json_type_str = g.table.get_type_symbol(node.args[0].typ).name
+		} else {
+			g.insert_before('// json.decode')
+			ast_type := node.args[0].expr as ast.Type
+			// `json.decode(User, s)` => json.decode_User(s)
+			sym := g.table.get_type_symbol(ast_type.typ)
+			name += '_' + sym.name
+		}
 	}
 	if node.is_c {
 		// Skip "C."
@@ -397,8 +407,8 @@ fn (mut g Gen) fn_call(node ast.CallExpr) {
 	} else {
 		name = c_name(name)
 	}
-	if g.is_json_fn {
-		// `json__decode` => `json__decode_User`
+	if is_json_encode {
+		// `json__encode` => `json__encode_User`
 		name += '_' + json_type_str
 	}
 	// Generate tmp vars for values that have to be freed.
@@ -476,14 +486,25 @@ fn (mut g Gen) fn_call(node ast.CallExpr) {
 		pafn := g.fn_decl.name.after('.')
 		mut pamod := g.fn_decl.name.all_before_last('.')
 		if pamod == pafn {
-			pamod = if g.fn_decl.is_builtin { 'builtin' } else { 'main' }
+			pamod = if g.fn_decl.is_builtin {
+				'builtin'
+			} else {
+				'main'
+			}
 		}
 		g.write('panic_debug($paline, tos3("$pafile"), tos3("$pamod"), tos3("$pafn"),  ')
 		g.call_args(node.args, node.expected_arg_types)
 		g.write(')')
 	} else {
 		g.write('${name}(')
-		g.call_args(node.args, node.expected_arg_types)
+		if is_json_decode {
+			g.write('json__json_parse(')
+			// Skip the first argument in json.decode which is a type
+			// its name was already used to generate the function call
+			g.call_args(node.args[1..], node.expected_arg_types)
+		} else {
+			g.call_args(node.args, node.expected_arg_types)
+		}
 		g.write(')')
 	}
 	// if node.or_block.stmts.len > 0 {
diff --git a/vlib/v/gen/json.v b/vlib/v/gen/json.v
index 6e19efcafc..f0d5feff23 100644
--- a/vlib/v/gen/json.v
+++ b/vlib/v/gen/json.v
@@ -31,8 +31,9 @@ fn (mut g Gen) gen_json_for_type(typ table.Type) {
 	// Code gen decoder
 	dec_fn_name := js_dec_name(sym.name)
 	dec.writeln('
-Option ${dec_fn_name}(cJSON* root, $styp* res) {
-//  $styp res;
+//Option ${dec_fn_name}(cJSON* root, $styp* res) {
+Option ${dec_fn_name}(cJSON* root) {
+  $styp res;
   if (!root) {
     const char *error_ptr = cJSON_GetErrorPtr();
     if (error_ptr != NULL)	{
@@ -70,7 +71,7 @@ cJSON* ${enc_fn_name}($styp val) {
 			g.gen_json_for_type(field.typ)
 			dec_name := js_dec_name(field_type)
 			if is_js_prim(field_type) {
-				dec.writeln(' res->$field.name = $dec_name (js_get(' + 'root, "$name"))')
+				dec.writeln(' res . $field.name = $dec_name (js_get(' + 'root, "$name"))')
 			} else {
 				dec.writeln(' $dec_name (js_get(root, "$name"), & (res->$field.name))')
 			}
@@ -80,7 +81,7 @@ cJSON* ${enc_fn_name}($styp val) {
 	}
 	// cJSON_delete
 	// p.cgen.fns << '$dec return opt_ok(res); \n}'
-	dec.writeln('return opt_ok(res, sizeof(*res)); \n}')
+	dec.writeln('return opt_ok(&res, sizeof(res)); \n}')
 	enc.writeln('\treturn o;\n}')
 	g.definitions.writeln(dec.str())
 	g.gowrappers.writeln(enc.str())
diff --git a/vlib/v/parser/fn.v b/vlib/v/parser/fn.v
index e2fa7e7fbd..6c650847c4 100644
--- a/vlib/v/parser/fn.v
+++ b/vlib/v/parser/fn.v
@@ -20,6 +20,11 @@ pub fn (mut p Parser) call_expr(is_c, is_js bool, mod string) ast.CallExpr {
 	} else {
 		name
 	}
+	if fn_name == 'json.decode' {
+		// Makes name_expr() parse the type (`User` in `json.decode(User, txt)`)`
+		p.inside_is = true
+		p.expr_mod = ''
+	}
 	p.check(.lpar)
 	args := p.call_args()
 	last_pos := p.tok.position()
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index cccfc1b905..2692114c96 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -32,7 +32,7 @@ mut:
 	mod               string // current module name
 	attr              string
 	attr_ctdefine     string
-	expr_mod          string
+	expr_mod          string // for constructing full type names in parse_type()
 	scope             &ast.Scope
 	global_scope      &ast.Scope
 	imports           map[string]string
@@ -104,7 +104,7 @@ pub fn parse_file(path string, b_table &table.Table, comments_mode scanner.Comme
 	for {
 		if p.tok.kind == .eof {
 			if p.pref.is_script && !p.pref.is_test && p.mod == 'main' && !have_fn_main(stmts) {
-				stmts << ast.FnDecl {
+				stmts << ast.FnDecl{
 					name: 'main'
 					file: p.file_name
 					return_type: table.void_type
@@ -355,7 +355,7 @@ pub fn (mut p Parser) top_stmt() ast.Stmt {
 		}
 		else {
 			if p.pref.is_script && !p.pref.is_test {
-				p.scanner.add_fn_main_and_rescan(p.tok.pos-1)
+				p.scanner.add_fn_main_and_rescan(p.tok.pos - 1)
 				p.read_first_token()
 				return p.top_stmt()
 			} else {
@@ -588,8 +588,9 @@ pub fn (mut p Parser) name_expr() ast.Expr {
 		p.inside_is = false
 		// get type position before moving to next
 		type_pos := p.tok.position()
+		typ := p.parse_type()
 		return ast.Type{
-			typ: p.parse_type()
+			typ: typ
 			pos: type_pos
 		}
 	}
@@ -1062,8 +1063,8 @@ fn (mut p Parser) return_stmt() ast.Return {
 
 // left hand side of `=` or `:=` in `a,b,c := 1,2,3`
 fn (mut p Parser) global_decl() ast.GlobalDecl {
-	if !p.pref.translated && !p.pref.is_livemain && !p.builtin_mod && !p.pref.building_v && p.mod !=
-		'ui' && p.mod != 'gg2' && p.mod != 'uiold' && !os.getwd().contains('/volt') && !p.pref.enable_globals {
+	if !p.pref.translated && !p.pref.is_livemain && !p.builtin_mod && !p.pref.building_v &&
+		p.mod != 'ui' && p.mod != 'gg2' && p.mod != 'uiold' && !os.getwd().contains('/volt') && !p.pref.enable_globals {
 		p.error('use `v --enable-globals ...` to enable globals')
 	}
 	p.next()