diff --git a/src/vigenere_cipher_helper.py b/src/vigenere_cipher_helper.py
index fb5401a..b560a7f 100644
--- a/src/vigenere_cipher_helper.py
+++ b/src/vigenere_cipher_helper.py
@@ -17,11 +17,16 @@ class VigenereCipher(object):
         new_text = []
 
         for l_text, l_key in zip(text, new_key):
-            if l_key in self.alphabet:
-                new_pos = self.alphabet.index(l_text) + self.alphabet.index(l_key)
+            if l_text in self.alphabet:
+                if l_key in self.alphabet:
+                    new_pos = (
+                        self.alphabet.index(l_text) + self.alphabet.index(l_key)
+                    ) % len(self.alphabet)
+                else:
+                    new_pos = self.alphabet.index(l_text)
+                new_text.append(self.alphabet[new_pos])
             else:
-                new_pos = self.alphabet.index(l_text)
-            new_text.append(self.alphabet[new_pos])
+                new_text.append(l_text)
         return "".join(new_text)
 
     def decode(self, text):
@@ -37,18 +42,15 @@ class VigenereCipher(object):
 
         new_text = []
 
-        for l_text in text:
-            for i, l_abc in enumerate(self.alphabet):
-                if l_text == l_abc:
-                    for l_key in new_key:
-                        for j, l_abc in enumerate(self.alphabet):
-                            if l_key == l_abc:
-                                new_pos = (i - j) % len(self.alphabet)
-                            else:
-                                new_pos = i
+        for l_text, l_key in zip(text, new_key):
+            if l_text in self.alphabet:
+                if l_key in self.alphabet:
+                    new_pos = (
+                        self.alphabet.index(l_text) - self.alphabet.index(l_key)
+                    ) % len(self.alphabet)
                 else:
-                    continue
-                for i, l_abc in enumerate(self.alphabet):
-                    if new_pos == i:
-                        new_text.append(l_abc)
+                    new_pos = self.alphabet.index(l_text)
+                new_text.append(self.alphabet[new_pos])
+            else:
+                new_text.append(l_text)
         return "".join(new_text)