diff --git a/packages/mobx-react/src/observerClass.ts b/packages/mobx-react/src/observerClass.ts
index a6b0b4a97..c428e8003 100644
--- a/packages/mobx-react/src/observerClass.ts
+++ b/packages/mobx-react/src/observerClass.ts
@@ -133,7 +133,7 @@ export function makeClassComponentObserver(
         admin.mounted = true
 
         // Component instance committed, prevent reaction disposal.
-        observerFinalizationRegistry.unregister(admin)
+        observerFinalizationRegistry.unregister(this)
 
         // We don't set forceUpdate before mount because it requires a reference to `this`,
         // therefore `this` could NOT be garbage collected before mount,