diff --git a/node_modules/spica/type.ts b/node_modules/spica/type.ts
index c11e7a7..969a841 100644
--- a/node_modules/spica/type.ts
+++ b/node_modules/spica/type.ts
@@ -1,4 +1,4 @@
-import { isArray, toString, ObjectGetPrototypeOf } from './alias';
+import { ObjectGetPrototypeOf, isArray, toString } from './alias';
 
 export type NonNull = {};
 type Falsy = undefined | false | 0 | 0n | '' | null | void;
@@ -238,9 +238,10 @@ export function type(value: unknown): string {
     case 'function':
       return 'Function';
     case 'object':
-      if (value === null) return 'null';
-      assert(value = value as object);
-      const tag: string = (value as object)[Symbol.toStringTag];
+      if (value === null || value === undefined) return 'null';
+      const tag: string = (value as {
+        [key in typeof Symbol.toStringTag]: string
+      })[Symbol.toStringTag];
       if (tag) return tag;
       switch (ObjectGetPrototypeOf(value)) {
         case ArrayPrototype: