diff --git a/packages/rolldown/src/app/utils/__tests__/cache.test.ts b/packages/rolldown/src/app/utils/__tests__/cache.test.ts
index 6092c376..f63332ba 100644
--- a/packages/rolldown/src/app/utils/__tests__/cache.test.ts
+++ b/packages/rolldown/src/app/utils/__tests__/cache.test.ts
@@ -22,6 +22,108 @@ describe('maybeWeakMap', () => {
     map.set(obj, 'b')
     expect(map.get(obj)).toBe('b')
   })
+
+  // -- tests for the fixed `set` routing --
+
+  it('stores object keys in _weakMap', () => {
+    const map = new MaybeWeakMap<object, string>()
+    const key = { id: 1 }
+    map.set(key, 'value')
+    expect(Reflect.get(map, '_weakMap').has(key)).toBe(true)
+    expect(Reflect.get(map, '_map').has(key)).toBe(false)
+    expect(map.get(key)).toBe('value')
+  })
+
+  it('stores function keys in _weakMap', () => {
+    const map = new MaybeWeakMap<() => void, string>()
+    const key = () => {}
+    map.set(key, 'value')
+    expect(Reflect.get(map, '_weakMap').has(key)).toBe(true)
+    expect(Reflect.get(map, '_map').has(key)).toBe(false)
+    expect(map.get(key)).toBe('value')
+  })
+
+  it('stores local symbol keys in _weakMap', () => {
+    const map = new MaybeWeakMap<symbol, string>()
+    const key = Symbol('local')
+    map.set(key, 'value')
+    expect(Reflect.get(map, '_weakMap').has(key)).toBe(true)
+    expect(Reflect.get(map, '_map').has(key)).toBe(false)
+    expect(map.get(key)).toBe('value')
+  })
+
+  it('stores primitive keys in _map', () => {
+    const map = new MaybeWeakMap<string | number | boolean | null | undefined, string>()
+    map.set('primitive', 'value')
+    map.set(42, 'number')
+    map.set(true, 'boolean')
+    map.set(null, 'null')
+    map.set(undefined, 'undefined')
+    expect(Reflect.get(map, '_map').get('primitive')).toBe('value')
+    expect(Reflect.get(map, '_map').get(42)).toBe('number')
+    expect(Reflect.get(map, '_map').get(true)).toBe('boolean')
+    expect(Reflect.get(map, '_map').get(null)).toBe('null')
+    expect(Reflect.get(map, '_map').get(undefined)).toBe('undefined')
+  })
+
+  it('stores global symbol keys in _map', () => {
+    const map = new MaybeWeakMap<symbol, string>()
+    const key = Symbol.for('global')
+    map.set(key, 'value')
+    expect(Reflect.get(map, '_map').has(key)).toBe(true)
+    expect(Reflect.get(map, '_weakMap').has(key)).toBe(false)
+    expect(map.get(key)).toBe('value')
+  })
+
+  it('getOrInsert stores object keys in _weakMap', () => {
+    const map = new MaybeWeakMap<object, string>()
+    const key = { id: 3 }
+    const result = map.getOrInsert(key, 'default')
+    expect(result).toBe('default')
+    expect(Reflect.get(map, '_weakMap').has(key)).toBe(true)
+    expect(Reflect.get(map, '_map').has(key)).toBe(false)
+  })
+
+  it('getOrInsertComputed stores object keys in _weakMap', () => {
+    const map = new MaybeWeakMap<object, number>()
+    const key = { id: 2 }
+    const result = map.getOrInsertComputed(key, () => 42)
+    expect(result).toBe(42)
+    expect(Reflect.get(map, '_weakMap').has(key)).toBe(true)
+    expect(Reflect.get(map, '_map').has(key)).toBe(false)
+  })
+
+  // -- regression tests for get/has/delete with primitive keys --
+
+  it('get should not throw for primitive keys', () => {
+    const map = new MaybeWeakMap<any, any>()
+    expect(map.get('primitive')).toBe(undefined)
+    expect(map.get(42)).toBe(undefined)
+    expect(map.get(null)).toBe(undefined)
+    expect(map.get(undefined)).toBe(undefined)
+    expect(map.get(true)).toBe(undefined)
+    expect(map.get(Symbol.for('global'))).toBe(undefined)
+  })
+
+  it('has should not throw for primitive keys', () => {
+    const map = new MaybeWeakMap<any, any>()
+    expect(map.has('primitive')).toBe(false)
+    expect(map.has(42)).toBe(false)
+    expect(map.has(null)).toBe(false)
+    expect(map.has(undefined)).toBe(false)
+    expect(map.has(true)).toBe(false)
+    expect(map.has(Symbol.for('global'))).toBe(false)
+  })
+
+  it('delete should not throw for primitive keys', () => {
+    const map = new MaybeWeakMap<any, any>()
+    expect(map.delete('primitive')).toBe(false)
+    expect(map.delete(42)).toBe(false)
+    expect(map.delete(null)).toBe(false)
+    expect(map.delete(undefined)).toBe(false)
+    expect(map.delete(true)).toBe(false)
+    expect(map.delete(Symbol.for('global'))).toBe(false)
+  })
 })
 
 describe('tupleMap', () => {
diff --git a/packages/rolldown/src/app/utils/cache.ts b/packages/rolldown/src/app/utils/cache.ts
index 4413f842..0c26df87 100644
--- a/packages/rolldown/src/app/utils/cache.ts
+++ b/packages/rolldown/src/app/utils/cache.ts
@@ -7,6 +7,18 @@
 export class MaybeWeakMap<K, V> implements WeakMap<any, V> {
   private _map: Map<K, V>
   private _weakMap: WeakMap<any, V>
+  private _isValidWeakMapKey(key: unknown): boolean {
+    switch (typeof key) {
+      case 'object':
+        return key !== null
+      case 'function':
+        return true
+      case 'symbol':
+        return Symbol.keyFor(key) === undefined
+      default:
+        return false
+    }
+  }
 
   constructor() {
     this._map = new Map()
@@ -16,27 +28,29 @@ export class MaybeWeakMap<K, V> implements WeakMap<any, V> {
   [Symbol.toStringTag]: string = 'MaybeWeakMap'
 
   delete(key: K): boolean {
-    if (this._weakMap.has(key))
+    if (this._isValidWeakMapKey(key))
       return this._weakMap.delete(key)
     return this._map.delete(key)
   }
 
   has(key: K): boolean {
-    if (this._weakMap.has(key))
-      return true
+    if (this._isValidWeakMapKey(key))
+      return this._weakMap.has(key)
     return this._map.has(key)
   }
 
   set(key: K, value: V): this {
-    if (this._weakMap.has(key))
+    if (this._isValidWeakMapKey(key)) {
       this._weakMap.set(key, value)
-    else
+    }
+    else {
       this._map.set(key, value)
+    }
     return this
   }
 
   get(key: K): V | undefined {
-    if (this._weakMap.has(key))
+    if (this._isValidWeakMapKey(key))
       return this._weakMap.get(key)
     return this._map.get(key)
   }