diff --git a/src/bpe_model_test.cc b/src/bpe_model_test.cc
index ccd0066..42d4062 100644
--- a/src/bpe_model_test.cc
+++ b/src/bpe_model_test.cc
@@ -12,11 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.!
 
-#include "bpe_model.h"
-
 #include <cstdio>
 #include <string>
 
+#include "bpe_model.h"
 #include "model_interface.h"
 #include "testharness.h"
 
diff --git a/src/sentencepiece_processor.h b/src/sentencepiece_processor.h
index ce7d61c..dfef468 100644
--- a/src/sentencepiece_processor.h
+++ b/src/sentencepiece_processor.h
@@ -98,11 +98,6 @@ class Status {
   struct Rep;
   std::unique_ptr<Rep> rep_;
 };
-
-// Redefine std::string for serialized_proto interface as Python's string is
-// a Unicode string. We can enforce the return value to be raw byte sequence
-// with SWIG's typemap.
-using bytes = std::string;
 }  // namespace util
 
 // SentencePieceProcessor:
@@ -176,6 +171,13 @@ enum class EncoderVersion {
                // just in case).
 };
 
+namespace util {
+// Redefine std::string for serialized_proto interface as Python's string is
+// a Unicode string. We can enforce the return value to be raw byte sequence
+// with SWIG's typemap.
+using bytes = std::string;
+}  // namespace util
+
 class SentencePieceProcessor {
  public:
   SentencePieceProcessor();
diff --git a/src/unigram_model_test.cc b/src/unigram_model_test.cc
index d6375e7..e8ea0c6 100644
--- a/src/unigram_model_test.cc
+++ b/src/unigram_model_test.cc
@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.!
 
-#include "unigram_model.h"
-
 #include <cmath>
 #include <map>
 #include <string>
@@ -24,6 +22,7 @@
 #include "testharness.h"
 #include "third_party/absl/strings/str_cat.h"
 #include "third_party/absl/strings/str_join.h"
+#include "unigram_model.h"
 #include "util.h"
 
 namespace sentencepiece {