diff --git a/src/protocol-detail/challenge.cpp b/src/protocol-detail/challenge.cpp
index aa0d884..3504115 100644
--- a/src/protocol-detail/challenge.cpp
+++ b/src/protocol-detail/challenge.cpp
@@ -59,5 +59,5 @@
   }
 }
 
-}  // namespace ndncert
-}  // namespace ndn
+} // namespace ndncert
+} // namespace ndn