diff --git a/test/test-computed-properties.js b/test/test-computed-properties.js
index a4453bf..869590d 100644
--- a/test/test-computed-properties.js
+++ b/test/test-computed-properties.js
@@ -213,6 +213,19 @@ it('does correct NaN checking', () => {
   assert(el.count === count);
 });
 
+it('resets compute validity on initialization to catch upgrade edge cases with internal, computed properties', () => {
+  const el = document.createElement('test-element');
+  el.setAttribute('a', '1');
+  el.setAttribute('b', '2');
+  assert(el.a === undefined);
+  assert(el.b === undefined);
+  assert(Number.isNaN(el.internal.c));
+  document.body.append(el);
+  assert(el.a === 1);
+  assert(el.b === 2);
+  assert(el.internal.c === 3);
+});
+
 it('cannot be written to from host', () => {
   const el = document.createElement('test-element');
   document.body.append(el);
diff --git a/x-element.js b/x-element.js
index 1af8cad..441ee4b 100644
--- a/x-element.js
+++ b/x-element.js
@@ -646,7 +646,7 @@ export default class XElement extends HTMLElement {
 
   static #initializeHost(host) {
     const hostInfo = XElement.#hosts.get(host);
-    const { initialized, invalidProperties } = hostInfo;
+    const { computeMap, initialized, invalidProperties } = hostInfo;
     if (initialized === false) {
       XElement.#upgradeOwnProperties(host);
       // Only reflect attributes when the element is connected.
@@ -661,6 +661,9 @@ export default class XElement extends HTMLElement {
           XElement.#setPropertyValue(host, property, property.default(host, property.initial()));
         }
         invalidProperties.add(property);
+        if (property.compute) {
+          computeMap.get(property).valid = false;
+        }
       }
       hostInfo.initialized = true;
       return true;