diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index 8bb14c16ba..abefafe27a 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -2911,12 +2911,13 @@ fn (mut g Gen) infix_expr(node ast.InfixExpr) {
 			if elem_sym.kind == .interface_ && node.right_type != info.elem_type {
 				g.interface_call(node.right_type, info.elem_type)
 			}
-			// if g.pref.autofree && info.elem_type == table.string_type {
-			if info.elem_type == table.string_type {
+			// if g.pref.autofree
+			needs_clone := info.elem_type == table.string_type && !g.is_builtin_mod
+			if needs_clone {
 				g.write('string_clone(')
 			}
 			g.expr_with_cast(node.right, node.right_type, info.elem_type)
-			if info.elem_type == table.string_type {
+			if needs_clone {
 				g.write(')')
 			}
 			if is_interface {