diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 6f24e11518de4b..d1735000ab0a06 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -3070,7 +3070,17 @@ fn (mut g Gen) gen_clone_assignment(var_type ast.Type, val ast.Expr, typ ast.Typ
 			if typ.share() == .shared_t {
 				g.write('(${shared_styp}*)__dup_shared_array(&(${shared_styp}){.mtx = {0}, .val =')
 			}
-			g.write(' array_clone_static_to_depth(')
+			is_sumtype := g.table.type_kind(var_type) == .sum_type
+			if is_sumtype {
+				variant_typ := g.typ(typ).replace('*', '')
+				fn_name := g.get_sumtype_casting_fn(typ, var_type)
+				g.write('${fn_name}(ADDR(${variant_typ}, array_clone_static_to_depth(')
+				if typ.is_ptr() {
+					g.write('*')
+				}
+			} else {
+				g.write(' array_clone_static_to_depth(')
+			}
 			g.expr(val)
 			if typ.share() == .shared_t {
 				g.write('->val')
@@ -3081,6 +3091,9 @@ fn (mut g Gen) gen_clone_assignment(var_type ast.Type, val ast.Expr, typ ast.Typ
 			if typ.share() == .shared_t {
 				g.write('}, sizeof(${shared_styp}))')
 			}
+			if is_sumtype {
+				g.write('))')
+			}
 		} else if right_sym.kind == .string {
 			// `str1 = str2` => `str1 = str2.clone()`
 			if var_type.has_flag(.option) {
diff --git a/vlib/v/tests/sumtypes/sumtype_map_set_test.v b/vlib/v/tests/sumtypes/sumtype_map_set_test.v
new file mode 100644
index 00000000000000..7c266ad0c2e874
--- /dev/null
+++ b/vlib/v/tests/sumtypes/sumtype_map_set_test.v
@@ -0,0 +1,29 @@
+module main
+
+pub type Value = f64 | []Value
+
+fn test_no_ref() {
+	mut m := map[string]Value{}
+	var := Value([Value(1.0), Value(2.0), Value(3.0)])
+	arr := (var as []Value)
+	m['var'] = arr
+	dump(m)
+	if item := m['var'] {
+		assert (item as []Value)[1] == Value(2.0)
+	} else {
+		assert false
+	}
+}
+
+fn test_ref() {
+	mut m := map[string]Value{}
+	var := Value([Value(1.0), Value(2.0), Value(3.0)])
+	arr := &(var as []Value)
+	m['var'] = arr
+	dump(m)
+	if item := m['var'] {
+		assert (item as []Value)[1] == Value(2.0)
+	} else {
+		assert false
+	}
+}