diff --git a/src/Umbraco.Infrastructure/Serialization/JsonBlockValueConverter.cs b/src/Umbraco.Infrastructure/Serialization/JsonBlockValueConverter.cs
index 71624b6529b0..b29e829266fe 100644
--- a/src/Umbraco.Infrastructure/Serialization/JsonBlockValueConverter.cs
+++ b/src/Umbraco.Infrastructure/Serialization/JsonBlockValueConverter.cs
@@ -1,4 +1,5 @@
 using System.Text.Json;
+using System.Text.Json.Nodes;
 using System.Text.Json.Serialization;
 using Umbraco.Cms.Core.Models.Blocks;
 using Umbraco.Extensions;
@@ -121,7 +122,17 @@ private static Type GetLayoutItemType(Type blockValueType)
     }
 
     private List<BlockItemData> DeserializeBlockItemData(ref Utf8JsonReader reader, JsonSerializerOptions options, Type typeToConvert, string propertyName)
-        => DeserializeListOf<BlockItemData>(ref reader, options, typeToConvert, propertyName);
+    {
+        try
+        {
+            return DeserializeListOf<BlockItemData>(ref reader, options, typeToConvert, propertyName);
+        }
+        catch (JsonException ex) when (ex.Path?.EndsWith(".values") is true)
+        {
+            // If we hit a JsonException due to the "values" property conflict, attempt the fallback deserialization
+            return FallbackBlockItemDataDeserialization(ref reader, options);
+        }
+    }
 
     private List<BlockItemVariation> DeserializeBlockVariation(ref Utf8JsonReader reader, JsonSerializerOptions options, Type typeToConvert, string propertyName)
         => DeserializeListOf<BlockItemVariation>(ref reader, options, typeToConvert, propertyName);
@@ -224,5 +235,38 @@ private void DeserializeAndSetLayout(ref Utf8JsonReader reader, JsonSerializerOp
             }
         }
     }
-}
 
+    [Obsolete("Only needed to support the old data schema. Remove in V18.")]
+    private static List<BlockItemData> FallbackBlockItemDataDeserialization(ref Utf8JsonReader reader, JsonSerializerOptions options)
+    {
+        JsonArray? arrayElement = JsonSerializer.Deserialize<JsonArray>(ref reader, options);
+
+        return arrayElement?
+            .Select(itemElement => DeserializeBlockItemData(itemElement, options))
+            .OfType<BlockItemData>()
+            .ToList() ?? [];
+    }
+
+    [Obsolete("Only needed to support the old data schema. Remove in V18.")]
+    private static BlockItemData? DeserializeBlockItemData(JsonNode? jsonNode, JsonSerializerOptions options)
+    {
+        if (jsonNode is not JsonObject jsonObject || jsonObject.ContainsKey("values") is false)
+        {
+            // Nothing to be done, just deserialize as usual
+            return jsonNode.Deserialize<BlockItemData>(options);
+        }
+
+        // Handle the "values" property conflict by extracting the "values" property first and adding it to the
+        // RawPropertyValues dictionary after deserialization
+        JsonNode? values = jsonObject["values"];
+        jsonObject.Remove("values");
+
+        BlockItemData? blockItemData = jsonObject.Deserialize<BlockItemData>(options);
+        if (blockItemData is not null)
+        {
+            blockItemData.RawPropertyValues["values"] = values.Deserialize<object?>(options);
+        }
+
+        return blockItemData;
+    }
+}
diff --git a/tests/Umbraco.Tests.UnitTests/Umbraco.Infrastructure/Serialization/JsonBlockValueConverterTests.cs b/tests/Umbraco.Tests.UnitTests/Umbraco.Infrastructure/Serialization/JsonBlockValueConverterTests.cs
index f48c286a91e0..4d76b2ad8731 100644
--- a/tests/Umbraco.Tests.UnitTests/Umbraco.Infrastructure/Serialization/JsonBlockValueConverterTests.cs
+++ b/tests/Umbraco.Tests.UnitTests/Umbraco.Infrastructure/Serialization/JsonBlockValueConverterTests.cs
@@ -470,4 +470,42 @@ public void Try_Deserialize_Unknown_Block_Layout_With_Nested_Array()
         var serializer = new SystemTextJsonSerializer(new DefaultJsonSerializerEncoderFactory());
         Assert.DoesNotThrow(() => serializer.Deserialize<BlockListValue>(json));
     }
+
+    /// <summary>
+    /// Test case that verifies the fix for https://github.com/umbraco/Umbraco-CMS/issues/20409.
+    /// </summary>
+    [Test]
+    public void Can_Deserialize_BlockGrid_With_Blocks_Using_Values_As_Property_Alias()
+    {
+        // Create a serialized BlockGridValue in Umbraco 13 format that has a block with a property alias "values".
+        var serialized = @"{
+   ""layout"":{
+      ""Umbraco.BlockList"":[
+         {
+            ""contentUdi"":""umb://element/6ad18441631140d48515ea0fc5b00425""
+         }
+      ]
+   },
+   ""contentData"":[
+      {
+         ""contentTypeKey"":""a1d1123c-289b-4a05-b33f-9f06cb723da1"",
+         ""udi"":""umb://element/6ad18441631140d48515ea0fc5b00425"",
+         ""text"":""Text"",
+         ""values"":""Values""
+      }
+   ],
+   ""settingsData"":[
+   ]
+}";
+
+        var serializer = new SystemTextJsonSerializer(new DefaultJsonSerializerEncoderFactory());
+        var deserialized = serializer.Deserialize<BlockGridValue>(serialized);
+
+        Assert.IsNotNull(deserialized);
+
+        Assert.AreEqual(1, deserialized.ContentData.Count);
+        Assert.AreEqual(2, deserialized.ContentData[0].RawPropertyValues.Count);
+        Assert.AreEqual("Text", deserialized.ContentData[0].RawPropertyValues["text"]);
+        Assert.AreEqual("Values", deserialized.ContentData[0].RawPropertyValues["values"]);
+    }
 }