diff --git a/vlib/compiler/aparser.v b/vlib/compiler/aparser.v
index 01b673fe0d..c139e019d3 100644
--- a/vlib/compiler/aparser.v
+++ b/vlib/compiler/aparser.v
@@ -850,6 +850,7 @@ fn (p mut Parser) type_decl() {
 		mut idx := 0
 		mut done := false
 		mut ctype_names := []string
+		mut sum_variants := []string
 		for {
 			// p.tok == .pipe {
 			idx++
@@ -862,14 +863,17 @@ fn (p mut Parser) type_decl() {
 			if p.pass == .main {
 				// Update the type's parent
 				// println('child=$child_type_name parent=$name')
-				mut t := p.find_type(child_type_name)
+				t := p.find_type(child_type_name)
 				if t.name == '' {
 					p.error('unknown type `$child_type_name`')
 				}
-				t.parent = name
-				p.table.rewrite_type(t)
-				p.cgen.consts << '#define SumType_$child_type_name $idx // DEF2'
+				p.cgen.consts << '#define SumType_${name}_$child_type_name $idx // DEF2'
 				ctype_names << child_type_name
+				sum_variants << if p.mod in ['builtin', 'main'] || child_type_name in builtin_types {
+					child_type_name
+				} else {
+					p.prepend_mod(child_type_name)
+				}
 			}
 			if done {
 				break
@@ -882,10 +886,7 @@ fn (p mut Parser) type_decl() {
 				// p.fgen_nl()
 			}
 		}
-		if p.pass == .decl {
-			p.table.sum_types << name
-			// println(p.table.sum_types)
-		}
+		p.table.sum_types[name] = sum_variants
 		// Register the actual sum type
 		// println('registering sum $name')
 		p.table.register_type(Type{
diff --git a/vlib/compiler/expression.v b/vlib/compiler/expression.v
index ade220f44b..cf1cb2a642 100644
--- a/vlib/compiler/expression.v
+++ b/vlib/compiler/expression.v
@@ -66,11 +66,10 @@ fn (p mut Parser) bool_expression() string {
 	// e.g. `return InfixExpr{}` in a function expecting `Expr`
 	if expected != typ && expected in p.table.sum_types { // TODO perf
 		//p.warn('SUM CAST exp=$expected typ=$typ p.exp=$p.expected_type')
-		T := p.table.find_type(typ)
-		if T.parent == expected {
+		if typ in p.table.sum_types[expected] {
 			p.cgen.set_placeholder(start_ph, '/*SUM TYPE CAST2*/ ($expected) { .obj = memdup( &($typ[]) { ')
 			tt := typ.all_after('_') // TODO
-			p.gen('}, sizeof($typ) ), .typ = SumType_${tt} }')//${val}_type }')
+			p.gen('}, sizeof($typ) ), .typ = SumType_${expected}_${tt} }')//${val}_type }')
 		}
 	}
 	// `as` cast
@@ -90,10 +89,8 @@ fn (p mut Parser) key_as(typ string, start_ph int) string {
 		p.error('casting `$typ` to `$cast_typ` is not needed')
 	}
 	if typ in p.table.sum_types {
-		T := p.table.find_type(cast_typ)
-		if T.parent != typ {
-			p.error('cannot cast `$typ` to `$cast_typ`. `$cast_typ` is not a variant of `$typ`' +
-			'parent=$T.parent')
+		if !(cast_typ in  p.table.sum_types[typ]) {
+			p.error('cannot cast `$typ` to `$cast_typ`. `$cast_typ` is not a variant of `$typ`')
 		}
 		p.cgen.set_placeholder(start_ph, '*($cast_typ*)')
 		p.gen('.obj')
@@ -102,7 +99,7 @@ fn (p mut Parser) key_as(typ string, start_ph int) string {
 		sum_type:= p.cgen.cur_line.all_after('*) (').replace('.obj', '.typ')
 
 		n := cast_typ.all_after('__')
-		p.cgen.insert_before('if (($sum_type != SumType_$n) {
+		p.cgen.insert_before('if (($sum_type != SumType_${typ}_$n) {
 puts("runtime error: $p.file_name:$p.scanner.line_nr cannot cast sum type `$typ` to `$n`");
 exit(1);
 }
diff --git a/vlib/compiler/if_match.v b/vlib/compiler/if_match.v
index 04c3200f0e..3f0a6004c0 100644
--- a/vlib/compiler/if_match.v
+++ b/vlib/compiler/if_match.v
@@ -140,7 +140,7 @@ fn (p mut Parser) match_statement(is_expr bool) string {
 			if is_sum_type {
 				sum_child_type = p.get_type2().name
 				tt := sum_child_type.all_after('_')
-				p.gen('SumType_$tt')
+				p.gen('SumType_${typ}_$tt')
 				// println('got child $sum_child_type')
 				p.register_var(Var{
 					name: 'it'
diff --git a/vlib/compiler/table.v b/vlib/compiler/table.v
index 87fa93cecd..58cb29095c 100644
--- a/vlib/compiler/table.v
+++ b/vlib/compiler/table.v
@@ -21,8 +21,8 @@ pub mut:
 	// names        []Name
 	max_field_len         map[string]int // for vfmt: max_field_len['Parser'] == 12
 	generic_struct_params map[string][]string
-	tuple_variants map[string][]string // enum( Bool(BoolExpr) )
-	sum_types []string
+	tuple_variants		  map[string][]string // enum( Bool(BoolExpr) )
+	sum_types			  map[string][]string // SumType -> [Variants]
 }
 
 struct VargAccess {
@@ -191,6 +191,8 @@ const (
 	float_types = ['f32', 'f64']
 	reserved_type_param_names = ['R', 'S', 'T', 'U', 'W']
 	pointer_types = ['byte*', 'byteptr', 'char*', 'charptr', 'void*', 'voidptr', 'voidptr*', 'intptr']
+	builtin_types = ['int', 'i8', 'char', 'byte', 'i16', 'u16', 'u32', 'i64', 'u64',
+		'f64', 'f32', 'byteptr', 'charptr', 'voidptr', 'intptr', 'string', 'ustring']
 )
 
 fn is_number_type(typ string) bool {
@@ -745,8 +747,7 @@ fn (p mut Parser) check_types2(got_, expected_ string, throw bool) bool {
 		// Sum type
 		if expected in p.table.sum_types {
 			//println('checking sum')
-			child := p.table.find_type(got)
-			if child.parent == expected {
+			if got in p.table.sum_types[expected] {
 				//println('yep $expected')
 				return true
 			}
diff --git a/vlib/compiler/tests/type_test.v b/vlib/compiler/tests/type_test.v
index fc14fe6ef7..48a9761190 100644
--- a/vlib/compiler/tests/type_test.v
+++ b/vlib/compiler/tests/type_test.v
@@ -20,7 +20,9 @@ fn test_person_str() {
 
 struct Foo {}
 
-type Expr = Foo | BoolExpr |  BinExpr | UnaryExpr
+type Expr = Foo | BoolExpr |  BinExpr | UnaryExpr | DeclExprA | DeclExprB
+
+type DeclExpr = DeclExprA | DeclExprB
 
 struct BoolExpr {
 	foo int
@@ -31,6 +33,14 @@ struct BinExpr {
 	name string
 }
 
+struct DeclExprA {
+	name string
+}
+
+struct DeclExprB {
+	name string
+}
+
 fn expr1() Expr {
 	mut e := Expr{}
 	e = BinExpr{'binexpr'}
@@ -46,11 +56,14 @@ struct UnaryExpr {
 
 }
 
-
 fn handle_expr(e Expr) {
 
 }
 
+fn handle_decl_expr(de DeclExpr) {
+
+}
+
 fn parse_bool() BoolExpr {
 	return BoolExpr{}
 }
@@ -64,6 +77,10 @@ fn test_sum_type_cast() {
 fn test_sum_types() {
 	b := parse_bool()
 	handle_expr(b)
+
+	de := DeclExprA{}
+	handle_expr(de)
+	handle_decl_expr(de)
 }
 
 /*