diff --git a/src/Avalonia.Base/Utilities/SmallDictionary.cs b/src/Avalonia.Base/Utilities/SmallDictionary.cs
index ea6769c1ba..fbb22058a6 100644
--- a/src/Avalonia.Base/Utilities/SmallDictionary.cs
+++ b/src/Avalonia.Base/Utilities/SmallDictionary.cs
@@ -77,9 +77,17 @@ internal struct InlineDictionary<TKey, TValue> : IEnumerable<KeyValuePair<TKey,
         }
         else
         {
-            // We have a single element, upgrade to array
+            // We have a single element, check if we should update the value.
+            var data = (TKey)_data;
+            if (data == key && overwrite)
+            {
+                _value = value;
+
+                return;
+            }
+            // If we do not replace it, upgrade to array.
             arr = new KeyValuePair[6];
-            arr[0] = new KeyValuePair((TKey)_data, _value);
+            arr[0] = new KeyValuePair(data, _value);
             arr[1] = new KeyValuePair(key, value);
             _data = arr;
             _value = default;
diff --git a/tests/Avalonia.Base.UnitTests/Utilities/InlineDictionaryTests.cs b/tests/Avalonia.Base.UnitTests/Utilities/InlineDictionaryTests.cs
index af47d2726a..760d56fb58 100644
--- a/tests/Avalonia.Base.UnitTests/Utilities/InlineDictionaryTests.cs
+++ b/tests/Avalonia.Base.UnitTests/Utilities/InlineDictionaryTests.cs
@@ -8,6 +8,17 @@ namespace Avalonia.Base.UnitTests.Utilities;
 
 public class InlineDictionaryTests
 {
+    [Fact]
+    public void Set_Twice_With_Single_Item_Works()
+    {
+        var dic = new InlineDictionary<string, int>();
+        dic["foo"] = 1;
+        Assert.Equal(1, dic["foo"]);
+
+        dic["foo"] = 2;
+        Assert.Equal(2, dic["foo"]);
+    }
+
     [Fact]
     public void Enumeration_After_Add_With_Internal_Array_Works()
     {