diff --git a/src/ObservableCollections/ObservableStack.cs b/src/ObservableCollections/ObservableStack.cs
index 78fea38..49814b9 100644
--- a/src/ObservableCollections/ObservableStack.cs
+++ b/src/ObservableCollections/ObservableStack.cs
@@ -166,7 +166,7 @@ namespace ObservableCollections
             }
         }
 
-        public bool TryPeek([MaybeNullWhen(false)] T result)
+        public bool TryPeek([MaybeNullWhen(false)] out T result)
         {
             lock (SyncRoot)
             {
@@ -212,4 +212,4 @@ namespace ObservableCollections
             return GetEnumerator();
         }
     }
-}
\ No newline at end of file
+}