diff --git a/Extensions.Test/CollectionExtensionsTests.cs b/Extensions.Test/CollectionExtensionsTests.cs
index 9fff389..38e3ba0 100644
--- a/Extensions.Test/CollectionExtensionsTests.cs
+++ b/Extensions.Test/CollectionExtensionsTests.cs
@@ -239,4 +239,24 @@ public void ReplaceWithNewItemsContainingNullsReplacesCorrectly()
 
 		CollectionAssert.AreEqual(new List<string?> { "x", null, "z" }, collection);
 	}
+
+	[TestMethod]
+	public void ReplaceWithLazyQueryOverSameCollectionKeepsMatchingItems()
+	{
+		List<int> collection = [1, 2, 3, 4];
+
+		collection.ReplaceWith(collection.Where(x => x > 2));
+
+		CollectionAssert.AreEqual(new List<int> { 3, 4 }, collection);
+	}
+
+	[TestMethod]
+	public void ReplaceWithSameCollectionKeepsItems()
+	{
+		List<int> collection = [1, 2, 3];
+
+		collection.ReplaceWith(collection);
+
+		CollectionAssert.AreEqual(new List<int> { 1, 2, 3 }, collection);
+	}
 }
diff --git a/Extensions/CollectionExtensions.cs b/Extensions/CollectionExtensions.cs
index 4d65af0..295812d 100644
--- a/Extensions/CollectionExtensions.cs
+++ b/Extensions/CollectionExtensions.cs
@@ -62,7 +62,9 @@ public static void ReplaceWith<T>(this ICollection<T> oldItems, IEnumerable<T> n
 		}
 #pragma warning restore KTSU0004 // Use Ensure.NotNull instead of manual null check
 
+		// Materialize first: newItems may be the collection itself or a lazy query over it, which Clear would empty
+		T[] snapshot = [.. newItems];
 		oldItems.Clear();
-		oldItems.AddFrom(newItems);
+		oldItems.AddFrom(snapshot);
 	}
 }