diff --git a/packages/@ember/-internals/metal/lib/observer.ts b/packages/@ember/-internals/metal/lib/observer.ts
index 2de6b2887f1..67b5fb678d8 100644
--- a/packages/@ember/-internals/metal/lib/observer.ts
+++ b/packages/@ember/-internals/metal/lib/observer.ts
@@ -96,7 +96,7 @@ export function activateObserver(target: object, eventName: string, sync = false
   if (activeObservers.has(eventName)) {
     activeObservers.get(eventName)!.count++;
   } else {
-    let [path] = eventName.split(':');
+    let path = eventName.substring(0, eventName.lastIndexOf(':'));
     let tag = getChainTagsForKey(target, path, tagMetaFor(target), peekMeta(target));
 
     activeObservers.set(eventName, {
diff --git a/packages/@ember/-internals/metal/tests/observer_test.js b/packages/@ember/-internals/metal/tests/observer_test.js
index 161a535df06..1a78e8ea0c7 100644
--- a/packages/@ember/-internals/metal/tests/observer_test.js
+++ b/packages/@ember/-internals/metal/tests/observer_test.js
@@ -87,6 +87,21 @@ moduleFor(
       assert.equal(count, 1, 'should have invoked observer');
     }
 
+    async ['@test observer supports keys with colons'](assert) {
+      obj = {};
+      let count = 0;
+
+      addObserver(obj, 'foo:bar:baz', function () {
+        assert.equal(get(obj, 'foo:bar:baz'), 'bar', 'should invoke AFTER value changed');
+        count++;
+      });
+
+      set(obj, 'foo:bar:baz', 'bar');
+      await runLoopSettled();
+
+      assert.equal(count, 1, 'should have invoked observer');
+    }
+
     async ['@test observer should fire when dependent property is modified'](assert) {
       obj = { bar: 'bar' };
       defineProperty(