@@ -452,6 +452,7 @@
       "captureError",
       "catchError",
       "checkGuards",
+      "checkOutletNameUniqueness",
       "checkSecurityContext",
       "checkStable",
       "classIndexOf",
 
@@ -228,11 +228,6 @@ export class Recognizer {
     // multiple activated results for the same outlet. We should merge the children of
     // these results so the final return value is only one `TreeNode` per outlet.
     const mergedChildren = mergeEmptyPathMatches(children);
-    if (typeof ngDevMode === 'undefined' || ngDevMode) {
-      // This should really never happen - we are only taking the first match for each
-      // outlet and merge the empty path matches.
-      checkOutletNameUniqueness(mergedChildren);
-    }
     sortActivatedRouteSnapshots(mergedChildren);
     return mergedChildren;
   }
@@ -585,11 +580,13 @@ function mergeEmptyPathMatches(
     const mergedChildren = mergeEmptyPathMatches(mergedNode.children);
     result.push(new TreeNode(mergedNode.value, mergedChildren));
   }
-  return result.filter((n) => !mergedNodes.has(n));
+  const merged = result.filter((n) => !mergedNodes.has(n));
+  checkOutletNameUniqueness(merged);
+  return merged;
 }
 
 function checkOutletNameUniqueness(nodes: TreeNode<ActivatedRouteSnapshot>[]): void {
-  const names: {[k: string]: ActivatedRouteSnapshot} = {};
+  const names: {[k: string]: ActivatedRouteSnapshot} = Object.create(null);
   nodes.forEach((n) => {
     const routeWithSameOutletName = names[n.value.outlet];
     if (routeWithSameOutletName) {
 
@@ -1179,6 +1179,44 @@ describe('recognize', () => {
       }
     });
   });
+
+  describe('outlet name uniqueness', () => {
+    // The two `detail` matches merge into one node, so the duplicate is among its children.
+    it('rejects duplicates that appear only after empty path matches are merged', async () => {
+      await expectAsync(
+        recognize(
+          [
+            {
+              path: 'a',
+              children: [
+                {path: '', outlet: 'detail', children: [{path: ':id', component: ComponentA}]},
+              ],
+            },
+          ],
+          'a/(detail:1//x:/(detail:2))',
+        ),
+      ).toBeRejectedWithError(/Two segments cannot have the same outlet name: '1' and '2'/);
+    });
+
+    it('does not treat an outlet named after an Object member as a duplicate', async () => {
+      const s = await recognize(
+        [
+          {
+            path: 'a',
+            children: [
+              {path: 'b', outlet: 'constructor', component: ComponentB},
+              {path: 'c', component: ComponentC},
+            ],
+          },
+        ],
+        'a/(c//constructor:b)',
+      );
+      const children = s.root.firstChild!.children;
+      expect(children.length).toBe(2);
+      checkActivatedRoute(children[0], 'c', {}, ComponentC);
+      checkActivatedRoute(children[1], 'b', {}, ComponentB, 'constructor');
+    });
+  });
 });
 
 function collectSnapshots(