diff --git a/packages/runtime-dom/__tests__/customElement.spec.ts b/packages/runtime-dom/__tests__/customElement.spec.ts
index 042ac68a7af..e56482c6174 100644
--- a/packages/runtime-dom/__tests__/customElement.spec.ts
+++ b/packages/runtime-dom/__tests__/customElement.spec.ts
@@ -9,6 +9,7 @@ import {
   renderSlot,
   VueElement
 } from '../src'
+import { parseNumber } from '../src/apiCustomElement'
 
 describe('defineCustomElement', () => {
   const container = document.createElement('div')
@@ -394,3 +395,36 @@ describe('defineCustomElement', () => {
     })
   })
 })
+
+describe('parseNumber', () => {
+  it('handles strings', () => {
+    expect(parseNumber('')).toBe('')
+    expect(parseNumber(null)).toBe('')
+    expect(parseNumber('Something else')).toBe('Something else')
+  })
+
+  it('numbers', () => {
+    expect(parseNumber('0')).toBe(0)
+    expect(parseNumber('1')).toBe(1)
+    expect(parseNumber('1.1')).toBe(1.1)
+    expect(parseNumber('123e-1')).toBe(12.3)
+    expect(parseNumber('Infinity')).toBe(Infinity)
+  })
+
+  it('NaN', () => {
+    expect(parseNumber('NaN')).toBeNaN()
+    expect(parseNumber('nan')).not.toBeNaN()
+  })
+
+  // all of these are handled by Number
+  it('string non decimal bases', () => {
+    expect(parseNumber('0b0')).toBe(0)
+    expect(parseNumber('0b1')).toBe(1)
+
+    expect(parseNumber('0o3')).toBe(3)
+    expect(parseNumber('0o0')).toBe(0)
+
+    expect(parseNumber('0x0')).toBe(0)
+    expect(parseNumber('0xf')).toBe(15)
+  })
+})
diff --git a/packages/runtime-dom/src/apiCustomElement.ts b/packages/runtime-dom/src/apiCustomElement.ts
index ca29a436c72..f43d75deea8 100644
--- a/packages/runtime-dom/src/apiCustomElement.ts
+++ b/packages/runtime-dom/src/apiCustomElement.ts
@@ -21,7 +21,7 @@ import {
   ConcreteComponent,
   ComponentOptions
 } from '@vue/runtime-core'
-import { camelize, extend, hyphenate, isArray, toNumber } from '@vue/shared'
+import { camelize, extend, hyphenate, isArray } from '@vue/shared'
 import { hydrate, render } from '.'
 
 export type VueElementConstructor<P = {}> = {
@@ -246,7 +246,7 @@ export class VueElement extends BaseClass {
   }
 
   protected _setAttr(key: string) {
-    this._setProp(camelize(key), toNumber(this.getAttribute(key)), false)
+    this._setProp(camelize(key), parseNumber(this.getAttribute(key)), false)
   }
 
   /**
@@ -342,3 +342,10 @@ export class VueElement extends BaseClass {
     }
   }
 }
+
+export function parseNumber(value: string | null): number | string {
+  // for Number('') and Number(null) as they both become 0
+  if (!value) return ''
+  const casted = Number(value)
+  return value === 'NaN' || !Number.isNaN(casted) ? casted : value
+}