diff --git a/Containers.Test/ContiguousMapTests.cs b/Containers.Test/ContiguousMapTests.cs
index 5a0659b..42f20f2 100644
--- a/Containers.Test/ContiguousMapTests.cs
+++ b/Containers.Test/ContiguousMapTests.cs
@@ -157,6 +157,22 @@ public void Indexer_Set_UpdatesValue()
 		Assert.AreEqual(1, map.Count); // Count should not change
 	}
 
+	[TestMethod]
+	public void Indexer_SetExistingKeyWithDifferentSpelling_KeepsOriginalKey()
+	{
+		// Arrange
+		ContiguousMap<string, int> map = new(StringComparer.OrdinalIgnoreCase) { ["Apple"] = 1 };
+
+		// Act
+		map["APPLE"] = 2;
+
+		// Assert
+		Assert.AreSequenceEqual(["Apple"], map.Keys);
+		Assert.AreEqual("Apple", map.AsSpan()[0].Key);
+		Assert.AreEqual(new KeyValuePair<string, int>("Apple", 2), map.Single());
+		Assert.AreEqual(2, map["apple"]);
+	}
+
 	[TestMethod]
 	public void Indexer_SetNewKey_AddsKeyValuePair()
 	{
diff --git a/Containers/ContiguousMap.cs b/Containers/ContiguousMap.cs
index b72142a..299d367 100644
--- a/Containers/ContiguousMap.cs
+++ b/Containers/ContiguousMap.cs
@@ -174,8 +174,8 @@ public TValue this[TKey key]
 
 			if (keyToIndex.TryGetValue(key, out int index))
 			{
-				// Key exists, update the value
-				items[index] = new Entry(key, value);
+				// Key exists, update the value and keep the key that was stored first
+				items[index] = new Entry(items[index].Key, value);
 			}
 			else
 			{