diff --git a/aos/stl_mutex/stl_mutex_test.cc b/aos/stl_mutex/stl_mutex_test.cc
index 5e88c56..5343974 100644
--- a/aos/stl_mutex/stl_mutex_test.cc
+++ b/aos/stl_mutex/stl_mutex_test.cc
@@ -4,8 +4,7 @@
 
 #include "aos/die.h"
 
-namespace aos {
-namespace testing {
+namespace aos::testing {
 
 class StlMutexDeathTest : public ::testing::Test {
  protected:
@@ -65,5 +64,4 @@
   EXPECT_DEATH(mutex.unlock(), ".*multiple unlock.*");
 }
 
-}  // namespace testing
-}  // namespace aos
+}  // namespace aos::testing