diff --git a/document_en/modint.md b/document_en/modint.md
index 700692d..2efbcee 100644
--- a/document_en/modint.md
+++ b/document_en/modint.md
@@ -35,6 +35,7 @@ If the mod is not fixed, you can use `modint` as follows.
 #include <iostream>
 
 using namespace std;
+using namespace atcoder;
 
 using mint = modint;
 // or: typedef modint mint;
diff --git a/document_ja/modint.md b/document_ja/modint.md
index b7e7e95..517c682 100644
--- a/document_ja/modint.md
+++ b/document_ja/modint.md
@@ -35,6 +35,7 @@ modがfixedでない場合は、`modint` を使用し以下のように書けま
 #include <iostream>
 
 using namespace std;
+using namespace atcoder;
 
 using mint = modint;
 // or: typedef modint mint;