diff --git a/internal/ceres/cubic_interpolation_test.cc b/internal/ceres/cubic_interpolation_test.cc
index 03b1aae..0200568 100644
--- a/internal/ceres/cubic_interpolation_test.cc
+++ b/internal/ceres/cubic_interpolation_test.cc
@@ -36,8 +36,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 static constexpr double kTolerance = 1e-12;
 
@@ -530,5 +529,4 @@
               kTolerance);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal