diff --git a/src/kana_transliteration.rs b/src/kana_transliteration.rs
index ffd4dba..dc1d053 100644
--- a/src/kana_transliteration.rs
+++ b/src/kana_transliteration.rs
@@ -384,7 +384,7 @@ pub fn transliterate_halfwidth_katakana_to_fullwidth_katakana(halfwidth: &str) -
             'ﾝ' => &['ン'],
             _ => &[c],
         };
-        result.push_str(out.iter().collect::<String>().as_str());
+        result.extend(out.iter().copied());
     }
 
     result
@@ -478,7 +478,7 @@ pub fn transliterate_fullwidth_katakana_to_halfwidth_katakana(fullwidth: &str) -
             _ => &[c],
         };
 
-        result.push_str(out.iter().collect::<String>().as_str());
+        result.extend(out.iter().copied());
     }
 
     result