diff --git a/sdk/ai/Azure.AI.Agents.Persistent/src/Custom/Streaming/RunStepDetailsUpdate.cs b/sdk/ai/Azure.AI.Agents.Persistent/src/Custom/Streaming/RunStepDetailsUpdate.cs
index 1d29269b9c67..74afbafef287 100644
--- a/sdk/ai/Azure.AI.Agents.Persistent/src/Custom/Streaming/RunStepDetailsUpdate.cs
+++ b/sdk/ai/Azure.AI.Agents.Persistent/src/Custom/Streaming/RunStepDetailsUpdate.cs
@@ -46,7 +46,7 @@ public IReadOnlyList<RunStepDeltaCodeInterpreterOutput> CodeInterpreterOutputs
         => _asCodeCall?.CodeInterpreter?.Outputs;
 
     /// <inheritdoc cref="RunStepDeltaFunction.Name"/>
-    public string FunctionName => _asFunctionCall.Function?.Name;
+    public string FunctionName => _asFunctionCall?.Function?.Name;
 
     /// <inheritdoc cref="RunStepDeltaFunction.Arguments"/>
     public string FunctionArguments => _asFunctionCall?.Function?.Arguments;