diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index 46dec82d1b..eea9bae317 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -749,12 +749,18 @@ pub:
 // New implementation of sum types
 pub struct SumTypeDecl {
 pub:
-	name      string
-	is_pub    bool
-	pos       token.Position
-	comments  []Comment
+	name     string
+	is_pub   bool
+	pos      token.Position
+	comments []Comment
 pub mut:
-	sub_types []table.Type
+	variants []SumTypeVariant
+}
+
+pub struct SumTypeVariant {
+pub:
+	typ table.Type
+	pos token.Position
 }
 
 pub struct FnTypeDecl {
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index bcd0acd844..aa633b1bdd 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -313,8 +313,11 @@ pub fn (mut c Checker) type_decl(node ast.TypeDecl) {
 		}
 		ast.SumTypeDecl {
 			c.check_valid_pascal_case(node.name, 'sum type', node.pos)
-			for typ in node.sub_types {
-				mut sym := c.table.get_type_symbol(typ)
+			for variant in node.variants {
+				if variant.typ.is_ptr() {
+					c.error('sum type cannot hold a reference type', variant.pos)
+				}
+				mut sym := c.table.get_type_symbol(variant.typ)
 				if sym.kind == .placeholder {
 					c.error("type `$sym.source_name` doesn't exist", node.pos)
 				} else if sym.kind == .interface_ {
diff --git a/vlib/v/checker/tests/sum_type_ref_variant_err.out b/vlib/v/checker/tests/sum_type_ref_variant_err.out
new file mode 100644
index 0000000000..d893a2b13e
--- /dev/null
+++ b/vlib/v/checker/tests/sum_type_ref_variant_err.out
@@ -0,0 +1,18 @@
+vlib/v/checker/tests/sum_type_ref_variant_err.vv:7:33: error: sum type cannot hold a reference type
+    5 |     foo string
+    6 | }
+    7 | type Alphabet1 = Abc | string | &Xyz
+      |                                 ~~~~
+    8 | type Alphabet2 = Abc | &Xyz | string
+    9 | type Alphabet3 = &Xyz | Abc | string
+vlib/v/checker/tests/sum_type_ref_variant_err.vv:8:24: error: sum type cannot hold a reference type
+    6 | }
+    7 | type Alphabet1 = Abc | string | &Xyz
+    8 | type Alphabet2 = Abc | &Xyz | string
+      |                        ~~~~
+    9 | type Alphabet3 = &Xyz | Abc | string
+vlib/v/checker/tests/sum_type_ref_variant_err.vv:9:18: error: sum type cannot hold a reference type
+    7 | type Alphabet1 = Abc | string | &Xyz
+    8 | type Alphabet2 = Abc | &Xyz | string
+    9 | type Alphabet3 = &Xyz | Abc | string
+      |                  ~~~~
\ No newline at end of file
diff --git a/vlib/v/checker/tests/sum_type_ref_variant_err.vv b/vlib/v/checker/tests/sum_type_ref_variant_err.vv
new file mode 100644
index 0000000000..def2a54995
--- /dev/null
+++ b/vlib/v/checker/tests/sum_type_ref_variant_err.vv
@@ -0,0 +1,9 @@
+struct Abc {
+    val string
+}
+struct Xyz {
+    foo string
+}
+type Alphabet1 = Abc | string | &Xyz
+type Alphabet2 = Abc | &Xyz | string
+type Alphabet3 = &Xyz | Abc | string
\ No newline at end of file
diff --git a/vlib/v/fmt/fmt.v b/vlib/v/fmt/fmt.v
index b8932f5584..42dce6ef57 100644
--- a/vlib/v/fmt/fmt.v
+++ b/vlib/v/fmt/fmt.v
@@ -547,8 +547,8 @@ pub fn (mut f Fmt) type_decl(node ast.TypeDecl) {
 			}
 			f.write('type $node.name = ')
 			mut sum_type_names := []string{}
-			for t in node.sub_types {
-				sum_type_names << f.table.type_to_str(t)
+			for t in node.variants {
+				sum_type_names << f.table.type_to_str(t.typ)
 			}
 			sum_type_names.sort()
 			for i, name in sum_type_names {
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index b43af05890..7cd9aba694 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -372,7 +372,7 @@ pub fn (mut g Gen) write_typeof_functions() {
 		if typ.kind == .sum_type {
 			sum_info := typ.info as table.SumType
 			tidx := g.table.find_type_idx(typ.name)
-			g.writeln('char * v_typeof_unionsumtype_${tidx}(int sidx) { /* $typ.name */ ')
+			g.writeln('char * v_typeof_sumtype_${tidx}(int sidx) { /* $typ.name */ ')
 			g.writeln('	switch(sidx) {')
 			g.writeln('		case $tidx: return "${util.strip_main_name(typ.name)}";')
 			for v in sum_info.variants {
@@ -1250,7 +1250,7 @@ fn (mut g Gen) for_in(it ast.ForInStmt) {
 }
 
 // use instead of expr() when you need to cast to union sum type (can add other casts also)
-fn (mut g Gen) union_expr_with_cast(expr ast.Expr, got_type table.Type, expected_type table.Type) {
+fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type table.Type, expected_type table.Type) {
 	// cast to sum type
 	if expected_type != table.void_type {
 		expected_is_ptr := expected_type.is_ptr()
@@ -1322,64 +1322,6 @@ fn (mut g Gen) union_expr_with_cast(expr ast.Expr, got_type table.Type, expected
 	g.expr(expr)
 }
 
-// use instead of expr() when you need to cast to sum type (can add other casts also)
-fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type table.Type, expected_type table.Type) {
-	sym := g.table.get_type_symbol(expected_type)
-	if sym.kind == .sum_type {
-		g.union_expr_with_cast(expr, got_type, expected_type)
-		return
-	}
-	// cast to sum type
-	if expected_type != table.void_type {
-		expected_is_ptr := expected_type.is_ptr()
-		expected_deref_type := if expected_is_ptr { expected_type.deref() } else { expected_type }
-		got_is_ptr := got_type.is_ptr()
-		got_deref_type := if got_is_ptr { got_type.deref() } else { got_type }
-		if g.table.sumtype_has_variant(expected_deref_type, got_deref_type) {
-			exp_styp := g.typ(expected_type)
-			got_styp := g.typ(got_type)
-			got_idx := got_type.idx()
-			got_sym := g.table.get_type_symbol(got_type)
-			if expected_is_ptr && got_is_ptr {
-				exp_der_styp := g.typ(expected_deref_type)
-				g.write('/* sum type cast */ ($exp_styp) memdup(&($exp_der_styp){._object = ')
-				g.expr(expr)
-				g.write(', .typ = $got_idx /* $got_sym.name */}, sizeof($exp_der_styp))')
-			} else if expected_is_ptr {
-				exp_der_styp := g.typ(expected_deref_type)
-				g.write('/* sum type cast */ ($exp_styp) memdup(&($exp_der_styp){._object = memdup(&($got_styp[]) {')
-				g.expr(expr)
-				g.write('}, sizeof($got_styp)), .typ = $got_idx /* $got_sym.name */}, sizeof($exp_der_styp))')
-			} else if got_is_ptr {
-				g.write('/* sum type cast */ ($exp_styp) {._object = ')
-				g.expr(expr)
-				g.write(', .typ = $got_idx /* $got_sym.name */}')
-			} else {
-				g.write('/* sum type cast */ ($exp_styp) {._object = memdup(&($got_styp[]) {')
-				g.expr(expr)
-				g.write('}, sizeof($got_styp)), .typ = $got_idx /* $got_sym.name */}')
-			}
-			return
-		}
-	}
-	// Generic dereferencing logic
-	expected_sym := g.table.get_type_symbol(expected_type)
-	got_is_ptr := got_type.is_ptr()
-	expected_is_ptr := expected_type.is_ptr()
-	neither_void := table.voidptr_type !in [got_type, expected_type]
-	if got_is_ptr && !expected_is_ptr && neither_void && expected_sym.kind !in [.interface_, .placeholder] {
-		got_deref_type := got_type.deref()
-		deref_sym := g.table.get_type_symbol(got_deref_type)
-		deref_will_match := expected_type in [got_type, got_deref_type, deref_sym.parent_idx]
-		got_is_opt := got_type.has_flag(.optional)
-		if deref_will_match || got_is_opt {
-			g.write('*')
-		}
-	}
-	// no cast
-	g.expr(expr)
-}
-
 // cestring returns a V string, properly escaped for embeddeding in a C string literal.
 fn cestring(s string) string {
 	return s.replace('\\', '\\\\').replace('"', "\'")
@@ -2646,7 +2588,7 @@ fn (mut g Gen) typeof_expr(node ast.TypeOf) {
 		// When encountering a .sum_type, typeof() should be done at runtime,
 		// because the subtype of the expression may change:
 		sum_type_idx := node.expr_type.idx()
-		g.write('tos3( /* $sym.name */ v_typeof_unionsumtype_${sum_type_idx}( (')
+		g.write('tos3( /* $sym.name */ v_typeof_sumtype_${sum_type_idx}( (')
 		g.expr(node.expr)
 		g.write(').typ ))')
 	} else if sym.kind == .array_fixed {
diff --git a/vlib/v/gen/fn.v b/vlib/v/gen/fn.v
index c4dd694c9c..70b5f63ad1 100644
--- a/vlib/v/gen/fn.v
+++ b/vlib/v/gen/fn.v
@@ -357,7 +357,7 @@ fn (mut g Gen) method_call(node ast.CallExpr) {
 		}
 	}
 	if left_sym.kind == .sum_type && node.name == 'type_name' {
-		g.write('tos3( /* $left_sym.name */ v_typeof_unionsumtype_${node.receiver_type}( (')
+		g.write('tos3( /* $left_sym.name */ v_typeof_sumtype_${node.receiver_type}( (')
 		g.expr(node.left)
 		g.write(').typ ))')
 		return
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index c05f8a7ba9..80cbc34609 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -1922,8 +1922,9 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 		p.error_with_pos('single letter capital names are reserved for generic template types.',
 			decl_pos)
 	}
-	mut sum_variants := []table.Type{}
+	mut sum_variants := []ast.SumTypeVariant{}
 	p.check(.assign)
+	mut type_pos := p.tok.position()
 	mut comments := []ast.Comment{}
 	if p.tok.kind == .key_fn {
 		// function type: `type mycallback fn(string, int)`
@@ -1940,17 +1941,31 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 	}
 	first_type := p.parse_type() // need to parse the first type before we can check if it's `type A = X | Y`
 	if p.tok.kind == .pipe {
+		mut type_end_pos := p.prev_tok.position()
+		type_pos = type_pos.extend(type_end_pos)
 		p.next()
-		sum_variants << first_type
+		sum_variants << ast.SumTypeVariant{
+			typ: first_type
+			pos: type_pos
+		}
 		// type SumType = A | B | c
 		for {
+			type_pos = p.tok.position()
 			variant_type := p.parse_type()
-			sum_variants << variant_type
+			// TODO: needs to be its own var, otherwise TCC fails because of a known stack error
+			prev_tok := p.prev_tok
+			type_end_pos = prev_tok.position()
+			type_pos = type_pos.extend(type_end_pos)
+			sum_variants << ast.SumTypeVariant{
+				typ: variant_type
+				pos: type_pos
+			}
 			if p.tok.kind != .pipe {
 				break
 			}
 			p.check(.pipe)
 		}
+		variant_types := sum_variants.map(it.typ)
 		prepend_mod_name := p.prepend_mod(name)
 		p.table.register_type_symbol(table.TypeSymbol{
 			kind: .sum_type
@@ -1958,7 +1973,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 			source_name: prepend_mod_name
 			mod: p.mod
 			info: table.SumType{
-				variants: sum_variants
+				variants: variant_types
 			}
 			is_public: is_pub
 		})
@@ -1966,7 +1981,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 		return ast.SumTypeDecl{
 			name: name
 			is_pub: is_pub
-			sub_types: sum_variants
+			variants: sum_variants
 			pos: decl_pos
 			comments: comments
 		}