diff --git a/csharp/src/Microsoft.ML.OnnxRuntime/InferenceSession.shared.cs b/csharp/src/Microsoft.ML.OnnxRuntime/InferenceSession.shared.cs
index c35c5f9111..b21d036f61 100644
--- a/csharp/src/Microsoft.ML.OnnxRuntime/InferenceSession.shared.cs
+++ b/csharp/src/Microsoft.ML.OnnxRuntime/InferenceSession.shared.cs
@@ -1060,6 +1060,7 @@ namespace Microsoft.ML.OnnxRuntime
             }
         }
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         private delegate void OrtCallbackDelegate(IntPtr userData, IntPtr[] outputs, uint numOutputs, IntPtr status);
 
         private static OrtCallbackDelegate ortCallback = new OrtCallbackDelegate(OrtCallback);