diff --git a/packages/runtime-dom/__tests__/customElement.spec.ts b/packages/runtime-dom/__tests__/customElement.spec.ts
index 6b9f7d1391e..df438d47eee 100644
--- a/packages/runtime-dom/__tests__/customElement.spec.ts
+++ b/packages/runtime-dom/__tests__/customElement.spec.ts
@@ -396,6 +396,38 @@ describe('defineCustomElement', () => {
       expect(e.value).toBe('hi')
     })
 
+    // #12214
+    test('Boolean prop with default true', async () => {
+      const E = defineCustomElement({
+        props: {
+          foo: {
+            type: Boolean,
+            default: true,
+          },
+        },
+        render() {
+          return String(this.foo)
+        },
+      })
+      customElements.define('my-el-default-true', E)
+      container.innerHTML = `<my-el-default-true></my-el-default-true>`
+      const e = container.childNodes[0] as HTMLElement & { foo: any },
+        shadowRoot = e.shadowRoot as ShadowRoot
+      expect(shadowRoot.innerHTML).toBe('true')
+      e.foo = undefined
+      await nextTick()
+      expect(shadowRoot.innerHTML).toBe('true')
+      e.foo = false
+      await nextTick()
+      expect(shadowRoot.innerHTML).toBe('false')
+      e.foo = null
+      await nextTick()
+      expect(shadowRoot.innerHTML).toBe('null')
+      e.foo = ''
+      await nextTick()
+      expect(shadowRoot.innerHTML).toBe('true')
+    })
+
     test('support direct setup function syntax with extra options', () => {
       const E = defineCustomElement(
         props => {
diff --git a/packages/runtime-dom/src/apiCustomElement.ts b/packages/runtime-dom/src/apiCustomElement.ts
index 6ddaf897130..c90c5725e17 100644
--- a/packages/runtime-dom/src/apiCustomElement.ts
+++ b/packages/runtime-dom/src/apiCustomElement.ts
@@ -232,6 +232,8 @@ export class VueElement
   private _styleChildren = new WeakSet()
   private _pendingResolve: Promise<void> | undefined
   private _parent: VueElement | undefined
+  private _removedAttributes = new Set<string>()
+
   /**
    * dev only
    */
@@ -466,8 +468,12 @@ export class VueElement
   protected _setAttr(key: string): void {
     if (key.startsWith('data-v-')) return
     const has = this.hasAttribute(key)
-    let value = has ? this.getAttribute(key) : REMOVAL
     const camelKey = camelize(key)
+    if (this._removedAttributes.has(camelKey)) {
+      if (!has) return
+      else this._removedAttributes.delete(camelKey)
+    }
+    let value = has ? this.getAttribute(key) : REMOVAL
     if (has && this._numberProps && this._numberProps[camelKey]) {
       value = toNumber(value)
     }
@@ -511,6 +517,7 @@ export class VueElement
           this.setAttribute(hyphenate(key), val + '')
         } else if (!val) {
           this.removeAttribute(hyphenate(key))
+          this._removedAttributes.add(key)
         }
       }
     }