diff --git a/lib/grnxx/db.cpp b/lib/grnxx/db.cpp
index a77c7d1..eadd2b7 100644
--- a/lib/grnxx/db.cpp
+++ b/lib/grnxx/db.cpp
@@ -138,7 +138,7 @@ unique_ptr<DB> open_db(Error *error,
     GRNXX_ERROR_SET(error, NOT_SUPPORTED_YET, "Not supported yet");
     return nullptr;
   }
-  std::unique_ptr<DB> db(new (nothrow) DB);
+  unique_ptr<DB> db(new (nothrow) DB);
   if (!db) {
     GRNXX_ERROR_SET(error, NO_MEMORY, "Memory allocation failed");
     return nullptr;
diff --git a/lib/grnxx/name.cpp b/lib/grnxx/name.cpp
index 80fab4a..d418fc8 100644
--- a/lib/grnxx/name.cpp
+++ b/lib/grnxx/name.cpp
@@ -24,7 +24,7 @@ bool Name::assign(Error *error, String name) {
     return false;
   }
 
-  std::unique_ptr<char[]> new_data(new (std::nothrow) char[name.size() + 1]);
+  unique_ptr<char[]> new_data(new (std::nothrow) char[name.size() + 1]);
   if (!new_data) {
     GRNXX_ERROR_SET(error, NO_MEMORY,
                     "Memory allocation failed: size = %" PRIi64, name.size());
diff --git a/lib/grnxx/name.hpp b/lib/grnxx/name.hpp
index 85920e1..c3929b9 100644
--- a/lib/grnxx/name.hpp
+++ b/lib/grnxx/name.hpp
@@ -42,7 +42,7 @@ class Name {
   bool assign(Error *error, String name);
 
  private:
-  std::unique_ptr<char[]> data_;
+  unique_ptr<char[]> data_;
   Int size_;
 
   static constexpr Int MIN_SIZE = 1;
diff --git a/lib/grnxx/table.cpp b/lib/grnxx/table.cpp
index e3a4935..80390de 100644
--- a/lib/grnxx/table.cpp
+++ b/lib/grnxx/table.cpp
@@ -477,7 +477,7 @@ unique_ptr<Table> Table::create(Error *error,
                                 DB *db,
                                 String name,
                                 const TableOptions &options) {
-  std::unique_ptr<Table> table(new Table);
+  unique_ptr<Table> table(new Table);
   table->db_ = db;
   if (!table->name_.assign(error, name)) {
     return nullptr;