Fix #4573

src/llvm_backend_expr.cpp

@@ -2145,6 +2145,12 @@ gb_internal lbValue lb_emit_conv(lbProcedure *p, lbValue value, Type *t) {
 			}
 		}
 		for (Type *vt : dst->Union.variants) {
+			if (src_type == t_llvm_bool && is_type_boolean(vt)) {
+				value = lb_emit_conv(p, value, vt);
+				lbAddr parent = lb_add_local_generated(p, t, true);
+				lb_emit_store_union_variant(p, parent.addr, value, vt);
+				return lb_addr_load(p, parent);
+			}
 			if (are_types_identical(src_type, vt)) {
 				lbAddr parent = lb_add_local_generated(p, t, true);
 				lb_emit_store_union_variant(p, parent.addr, value, vt);