diff --git a/src/ModelContextProtocol/Shared/McpSession.cs b/src/ModelContextProtocol/Shared/McpSession.cs
index 56f0674c..56d3791b 100644
--- a/src/ModelContextProtocol/Shared/McpSession.cs
+++ b/src/ModelContextProtocol/Shared/McpSession.cs
@@ -298,7 +298,18 @@ private void HandleMessageWithId(JsonRpcMessage message, JsonRpcMessageWithId me
         if (!_requestHandlers.TryGetValue(request.Method, out var handler))
         {
             LogNoHandlerFoundForRequest(EndpointName, request.Method);
-            throw new McpException($"Method '{request.Method}' is not available.", McpErrorCode.MethodNotFound);
+            await SendMessageAsync(new JsonRpcError
+            {
+                Id = request.Id,
+                JsonRpc = "2.0",
+                Error = new JsonRpcErrorDetail
+                {
+                    Message = $"{EndpointName} lacks capability to do {request.Method}",
+                    Code = (int) McpErrorCode.MethodNotFound,
+                },
+                RelatedTransport = request.RelatedTransport
+            }, cancellationToken).ConfigureAwait(false);
+            return null;
         }
 
         LogRequestHandlerCalled(EndpointName, request.Method);
@@ -764,4 +775,4 @@ private static TimeSpan GetElapsed(long startingTimestamp) =>
 
     [LoggerMessage(Level = LogLevel.Trace, Message = "{EndpointName} sending message. Message: '{Message}'.")]
     private partial void LogSendingMessageSensitive(string endpointName, string message);
-}
\ No newline at end of file
+}