diff --git a/AFJSONRPCClient/AFJSONRPCClient.m b/AFJSONRPCClient/AFJSONRPCClient.m
index 1c98687..6b41445 100755
--- a/AFJSONRPCClient/AFJSONRPCClient.m
+++ b/AFJSONRPCClient/AFJSONRPCClient.m
@@ -126,7 +126,10 @@ - (NSMutableURLRequest *)requestWithMethod:(NSString *)method
     payload[@"jsonrpc"] = @"2.0";
     payload[@"method"] = method;
     payload[@"params"] = parameters;
-    payload[@"id"] = [requestId description];
+    
+    if (requestId != [NSNull null]) {
+        payload[@"id"] = [requestId description];
+    }
 
     return [self.requestSerializer requestWithMethod:@"POST" URLString:[self.endpointURL absoluteString] parameters:payload error:nil];
 }