diff --git a/src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/Simplification/AbstractSimplificationService.cs b/src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/Simplification/AbstractSimplificationService.cs
index 2d7c6fd29bb93..758177a8a06ec 100644
--- a/src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/Simplification/AbstractSimplificationService.cs
+++ b/src/Workspaces/SharedUtilitiesAndExtensions/Workspace/Core/Simplification/AbstractSimplificationService.cs
@@ -219,9 +219,11 @@ async ValueTask ReduceOneNodeOrTokenAsync(
                                 ? nodeOrToken.Parent.ReplaceNode(nodeOrToken.AsNode()!, currentNodeOrToken.AsNode()!)
                                 : nodeOrToken.Parent.ReplaceToken(nodeOrToken.AsToken(), currentNodeOrToken.AsToken());
 
+                            Debug.Assert(replacedParent.ChildNodesAndTokens().Count(c => c.HasAnnotation(annotation)) == 1);
+
                             currentNodeOrToken = replacedParent
                                 .ChildNodesAndTokens()
-                                .Single(c => c.HasAnnotation(annotation));
+                                .First(c => c.HasAnnotation(annotation));
                         }
 
                         if (isNode)