diff --git a/src/vanilla.ts b/src/vanilla.ts
index dc19c875..da800e03 100644
--- a/src/vanilla.ts
+++ b/src/vanilla.ts
@@ -86,6 +86,9 @@ const buildProxyFunction = (
     !(x instanceof RegExp) &&
     !(x instanceof ArrayBuffer),
 
+  shouldTrapDefineProperty = (desc: PropertyDescriptor) =>
+    desc.configurable && desc.enumerable && desc.writable,
+
   defaultHandlePromise = <P extends Promise<any>>(
     promise: P & {
       status?: 'pending' | 'fulfilled' | 'rejected'
@@ -244,6 +247,50 @@ const buildProxyFunction = (
     const baseObject = Array.isArray(initialObject)
       ? []
       : Object.create(Object.getPrototypeOf(initialObject))
+    const trapSet = (
+      hasPrevValue: boolean,
+      prevValue: any,
+      prop: string | symbol,
+      value: any,
+      setValue: (nextValue: any) => void
+    ) => {
+      if (
+        hasPrevValue &&
+        (objectIs(prevValue, value) ||
+          (proxyCache.has(value) && objectIs(prevValue, proxyCache.get(value))))
+      ) {
+        return
+      }
+      removePropListener(prop)
+      if (isObject(value)) {
+        value = getUntracked(value) || value
+      }
+      let nextValue = value
+      if (value instanceof Promise) {
+        value
+          .then((v) => {
+            value.status = 'fulfilled'
+            value.value = v
+            notifyUpdate(['resolve', [prop], v])
+          })
+          .catch((e) => {
+            value.status = 'rejected'
+            value.reason = e
+            notifyUpdate(['reject', [prop], e])
+          })
+      } else {
+        if (!proxyStateMap.has(value) && canProxy(value)) {
+          nextValue = proxyFunction(value)
+        }
+        const childProxyState =
+          !refSet.has(nextValue) && proxyStateMap.get(nextValue)
+        if (childProxyState) {
+          addPropListener(prop, childProxyState)
+        }
+      }
+      setValue(nextValue)
+      notifyUpdate(['set', [prop], value, prevValue])
+    }
     const handler: ProxyHandler<T> = {
       deleteProperty(target: T, prop: string | symbol) {
         const prevValue = Reflect.get(target, prop)
@@ -257,44 +304,35 @@ const buildProxyFunction = (
       set(target: T, prop: string | symbol, value: any, receiver: object) {
         const hasPrevValue = Reflect.has(target, prop)
         const prevValue = Reflect.get(target, prop, receiver)
-        if (
-          hasPrevValue &&
-          (objectIs(prevValue, value) ||
-            (proxyCache.has(value) &&
-              objectIs(prevValue, proxyCache.get(value))))
-        ) {
-          return true
-        }
-        removePropListener(prop)
-        if (isObject(value)) {
-          value = getUntracked(value) || value
-        }
-        let nextValue = value
-        if (value instanceof Promise) {
-          value
-            .then((v) => {
-              value.status = 'fulfilled'
-              value.value = v
-              notifyUpdate(['resolve', [prop], v])
-            })
-            .catch((e) => {
-              value.status = 'rejected'
-              value.reason = e
-              notifyUpdate(['reject', [prop], e])
-            })
-        } else {
-          if (!proxyStateMap.has(value) && canProxy(value)) {
-            nextValue = proxyFunction(value)
-          }
-          const childProxyState =
-            !refSet.has(nextValue) && proxyStateMap.get(nextValue)
-          if (childProxyState) {
-            addPropListener(prop, childProxyState)
+        trapSet(hasPrevValue, prevValue, prop, value, (nextValue) => {
+          Reflect.set(target, prop, nextValue, receiver)
+        })
+        return true
+      },
+      defineProperty(
+        target: T,
+        prop: string | symbol,
+        desc: PropertyDescriptor
+      ) {
+        if (shouldTrapDefineProperty(desc)) {
+          const prevDesc = Reflect.getOwnPropertyDescriptor(target, prop)
+          if (!prevDesc || shouldTrapDefineProperty(prevDesc)) {
+            trapSet(
+              !!prevDesc && 'value' in prevDesc,
+              prevDesc?.value,
+              prop,
+              desc.value,
+              (nextValue) => {
+                Reflect.defineProperty(target, prop, {
+                  ...desc,
+                  value: nextValue,
+                })
+              }
+            )
+            return true
           }
         }
-        Reflect.set(target, prop, nextValue, receiver)
-        notifyUpdate(['set', [prop], value, prevValue])
-        return true
+        return Reflect.defineProperty(target, prop, desc)
       },
     }
     const proxyObject = newProxy(baseObject, handler)
@@ -333,6 +371,7 @@ const buildProxyFunction = (
     objectIs,
     newProxy,
     canProxy,
+    shouldTrapDefineProperty,
     defaultHandlePromise,
     snapCache,
     createSnapshot,
diff --git a/tests/class.test.tsx b/tests/class.test.tsx
index f40f8b00..31b0dae6 100644
--- a/tests/class.test.tsx
+++ b/tests/class.test.tsx
@@ -355,3 +355,31 @@ it('no extra re-renders with getters', async () => {
     getByText('sum: 2 (2)')
   })
 })
+
+it('support class fields (defineProperty semantics)', async () => {
+  class Base {
+    constructor() {
+      return proxy(this)
+    }
+  }
+  class CountClass extends Base {
+    counter = { count: 0 }
+  }
+  const obj = new CountClass()
+
+  const Counter = () => {
+    const snap = useSnapshot(obj)
+    return <div>count: {snap.counter.count}</div>
+  }
+
+  const { findByText } = render(
+    <StrictMode>
+      <Counter />
+    </StrictMode>
+  )
+
+  await findByText('count: 0')
+
+  obj.counter.count = 1
+  await findByText('count: 1')
+})