diff --git a/ciphers/rot13.py b/ciphers/rot13.py
index b367c3215127..2894101f2e4a 100644
--- a/ciphers/rot13.py
+++ b/ciphers/rot13.py
@@ -9,15 +9,17 @@ def dencrypt(s: str, n: int = 13) -> str:
     >>> dencrypt(s) == msg
     True
     """
-    out = ""
+    out = []
+
     for c in s:
         if "A" <= c <= "Z":
-            out += chr(ord("A") + (ord(c) - ord("A") + n) % 26)
+            out.append(chr(ord("A") + (ord(c) - ord("A") + n) % 26))
         elif "a" <= c <= "z":
-            out += chr(ord("a") + (ord(c) - ord("a") + n) % 26)
+            out.append(chr(ord("a") + (ord(c) - ord("a") + n) % 26))
         else:
-            out += c
-    return out
+            out.append(c)
+
+    return "".join(out)
 
 
 def main() -> None: