diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index b447463116..563eec7330 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -641,6 +641,8 @@ pub:
 pub struct TypeOf {
 pub:
 	expr Expr
+mut:
+	expr_type table.Type
 }
 
 pub struct LineComment {
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index e7f79c2675..177a8ad44b 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -779,6 +779,7 @@ pub fn (c mut Checker) expr(node ast.Expr) table.Type {
 			return it.typ
 		}
 		ast.TypeOf {
+			it.expr_type = c.expr(it.expr)
 			return table.string_type
 		}
 		/*
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index 2f5c539377..bc01fc35a1 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -107,12 +107,34 @@ pub fn (g mut Gen) init() {
 	g.definitions.writeln('\nstring _STR_TMP(const char*, ...);\n')
 	g.write_builtin_types()
 	g.write_typedef_types()
+	g.write_typeof_functions()
 	g.write_str_definitions()
 	g.write_sorted_types()
 	g.write_multi_return_types()
 	g.definitions.writeln('// end of definitions #endif')
 }
 
+pub fn (g mut Gen) write_typeof_functions() {
+	g.writeln('// >> typeof() support for sum types')
+	for typ in g.table.types {
+		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_sumtype_${tidx}(int sidx) { /* ${typ.name} */ ')
+			g.writeln('	switch(sidx) {')
+			g.writeln('		case $tidx: return "$typ.name";')
+			for v in sum_info.variants {
+				subtype := g.table.get_type_symbol(v)
+				g.writeln('		case $v: return "$subtype.name";')
+			}
+			g.writeln('		default: return "unknown ${typ.name}";')
+			g.writeln('	}')
+			g.writeln('}')
+		}
+	}
+	g.writeln('// << typeof() support for sum types')
+}
+
 // V type to C type
 pub fn (g mut Gen) typ(t table.Type) string {
 	nr_muls := table.type_nr_muls(t)
@@ -188,7 +210,7 @@ pub fn (g mut Gen) write_typedef_types() {
 			else {
 				continue
 			}
-	}
+		}
 	}
 }
 
@@ -772,7 +794,7 @@ fn (g mut Gen) free_scope_vars(pos int) {
 				else {
 					g.writeln('// other ' + t)
 				}
-	}
+			}
 			g.writeln('string_free($var.name); // autofreed')
 		}
 	}
@@ -1165,7 +1187,7 @@ fn (g mut Gen) expr(node ast.Expr) {
 			g.write('$type_idx /* $sym.name */')
 		}
 		ast.TypeOf {
-			g.write('tos3("TYPEOF_TODO")')
+			g.typeof_expr(it)
 		}
 		else {
 			// #printf("node=%d\n", node.typ);
@@ -1174,6 +1196,20 @@ fn (g mut Gen) expr(node ast.Expr) {
 	}
 }
 
+fn (g mut Gen) typeof_expr(node ast.TypeOf) {
+	sym := g.table.get_type_symbol(node.expr_type)
+	if sym.kind == .sum_type {
+		// When encountering a .sum_type, typeof() should be done at runtime,
+		// because the subtype of the expression may change:
+		sum_type_idx := table.type_idx( node.expr_type  )
+		g.write('tos3( /* ${sym.name} */ v_typeof_sumtype_${sum_type_idx}( (')
+		g.expr(node.expr)
+		g.write(').typ ))')
+	}else{
+		g.write('tos3("${sym.name}")')
+	}
+}
+
 fn (g mut Gen) infix_expr(node ast.InfixExpr) {
 	// println('infix_expr() op="$node.op.str()" line_nr=$node.pos.line_nr')
 	// g.write('/*infix*/')
diff --git a/vlib/v/tests/typeof_simple_types_test.v b/vlib/v/tests/typeof_simple_types_test.v
new file mode 100644
index 0000000000..e1f2a8701d
--- /dev/null
+++ b/vlib/v/tests/typeof_simple_types_test.v
@@ -0,0 +1,66 @@
+struct Abc {
+	x int
+}
+
+struct Xyz {
+	y int
+}
+
+struct XxYyZz {
+	y int
+}
+
+type MySumType = Abc | Xyz
+
+type AnotherSumType = XxYyZz | int
+
+type SuperSumType = MySumType | AnotherSumType | string
+
+fn test_typeof_for_builtin_int_types() {
+	assert typeof(1) == 'int'
+	assert typeof(i64(1)) == 'i64'
+	assert typeof(u32(1)) == 'u32'
+	assert typeof(u64(1)) == 'u64'
+}
+
+fn test_typeof_for_builtin_float_types() {
+	assert typeof(f32(1.0)) == 'f32'
+	assert typeof(1.0) == 'f64'
+}
+
+fn test_typeof_for_builtin_string_type() {
+	assert typeof('abc') == 'string'
+	assert typeof('/v/nv/vlib/v/tests/typeof_simple_types_test.v') == 'string'
+	assert typeof('22') == 'string'
+}
+
+fn test_typeof_for_structs() {
+	assert typeof(Abc{}) == 'Abc'
+	assert typeof(Xyz{}) == 'Xyz'
+}
+
+//
+fn mysumtype_typeof(x MySumType) string {
+	return typeof(x)
+}
+
+fn test_typeof_for_sumtypes() {
+	z_abc := Abc{}
+	z_xyz := Xyz{}
+	assert mysumtype_typeof(z_abc) == 'Abc'
+	assert mysumtype_typeof(z_xyz) == 'Xyz'
+}
+
+//
+fn supersumtype_typeof(x SuperSumType) string {
+	return typeof(x)
+}
+
+fn mst(x MySumType) MySumType {
+	return x
+}
+
+fn test_typeof_for_sumtypes_of_sumtypes() {
+	assert supersumtype_typeof('abc') == 'string'
+	assert supersumtype_typeof(mst(Abc{})) == 'MySumType'
+}