diff --git a/CHANGELOG.md b/CHANGELOG.md
index bbc3658e93..6f008adb45 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,9 +13,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Fixed a bug where TypeScript deserialization would fail on Uppercase properties.[#4479](https://github.com/microsoft/kiota/issues/4479)
 - Changed URI template generation to reuse templates when required templates are absent across operations.
-- Updated reserved name providers for Java and Php so that "object" can be escaped. 
-- Do not generate CS8603 warnings when enabling backing store in CSharp generation. 
+- Updated reserved name providers for Java and Php so that "object" can be escaped.
+- Do not generate CS8603 warnings when enabling backing store in CSharp generation.
 
 ## [1.13.0] - 2024-04-04
 
diff --git a/src/Kiota.Builder/Writers/TypeScript/CodeFunctionWriter.cs b/src/Kiota.Builder/Writers/TypeScript/CodeFunctionWriter.cs
index 0e54393520..d316d72f83 100644
--- a/src/Kiota.Builder/Writers/TypeScript/CodeFunctionWriter.cs
+++ b/src/Kiota.Builder/Writers/TypeScript/CodeFunctionWriter.cs
@@ -236,14 +236,13 @@ private void WriteDeserializerFunction(CodeFunction codeFunction, LanguageWriter
 
             foreach (var otherProp in properties)
             {
-                var keyName = !string.IsNullOrWhiteSpace(otherProp.SerializationName) ? otherProp.SerializationName.ToFirstCharacterLowerCase() : otherProp.Name.ToFirstCharacterLowerCase();
                 var suffix = otherProp.Name.Equals(primaryErrorMappingKey, StringComparison.Ordinal) ? primaryErrorMapping : string.Empty;
-                if (keyName.Equals(BackingStoreEnabledKey, StringComparison.Ordinal))
-                    writer.WriteLine($"\"{keyName}\": n => {{ {param.Name.ToFirstCharacterLowerCase()}.{otherProp.Name.ToFirstCharacterLowerCase()} = true;{suffix} }},");
+                if (otherProp.Kind is CodePropertyKind.BackingStore)
+                    writer.WriteLine($"\"{BackingStoreEnabledKey}\": n => {{ {param.Name.ToFirstCharacterLowerCase()}.{otherProp.Name.ToFirstCharacterLowerCase()} = true;{suffix} }},");
                 else
                 {
                     var defaultValueSuffix = GetDefaultValueLiteralForProperty(otherProp) is string dft && !string.IsNullOrEmpty(dft) ? $" ?? {dft}" : string.Empty;
-                    writer.WriteLine($"\"{keyName}\": n => {{ {param.Name.ToFirstCharacterLowerCase()}.{otherProp.Name.ToFirstCharacterLowerCase()} = n.{GetDeserializationMethodName(otherProp.Type, codeFunction)}{defaultValueSuffix};{suffix} }},");
+                    writer.WriteLine($"\"{otherProp.WireName}\": n => {{ {param.Name.ToFirstCharacterLowerCase()}.{otherProp.Name.ToFirstCharacterLowerCase()} = n.{GetDeserializationMethodName(otherProp.Type, codeFunction)}{defaultValueSuffix};{suffix} }},");
                 }
             }