diff --git a/Introduction to Coroutines and Channels/02_BlockingRequest.md b/Introduction to Coroutines and Channels/02_BlockingRequest.md
index 37fa8ce..b7da4b4 100644
--- a/Introduction to Coroutines and Channels/02_BlockingRequest.md	
+++ b/Introduction to Coroutines and Channels/02_BlockingRequest.md	
@@ -134,7 +134,7 @@ A possible solution:
 ```kotlin
 fun List<User>.aggregate(): List<User> =
     groupBy { it.login }
-        .map { (login, group) -> User(login, group.sumBy { it.contributions }) }
+        .map { (login, group) -> User(login, group.sumOf { it.contributions }) }
         .sortedByDescending { it.contributions }
 ```