diff --git a/onetimepad.py b/onetimepad.py
index 00e96ea..f027170 100644
--- a/onetimepad.py
+++ b/onetimepad.py
@@ -45,7 +45,7 @@ def _padfill(text, pad):
     padlines = pad.splitlines()
     textlines = _chunk_chars_into_lines(text, _get_textwidth(pad))
     for lineno, padline in enumerate(padlines[:]):
-        if _is_padline(lineno) or _is_cypherline(lineno):
+        if _is_padline(lineno) or _is_cipherline(lineno):
             continue
         else:
             padlines[lineno] = textlines.pop(0) if textlines[1:] else ''
@@ -64,8 +64,8 @@ def _is_txtline(lineno):
     return (lineno % 2 and not lineno % 3)
 
 
-def _is_cypherline(lineno):
-    return lineno % 3
+def _is_cipherline(lineno):
+    return lineno % PAD_MODULO
 
 
 def _mk_as_alpha():
diff --git a/test_onetimepad.py b/test_onetimepad.py
index 55eb536..ca8480d 100644
--- a/test_onetimepad.py
+++ b/test_onetimepad.py
@@ -28,9 +28,9 @@ class TestOneTimePad(unittest.TestCase):
             elif OT._is_txtline(lineno):
                 self.assertFalse(bool(len(line)),
                                  'text line {0} is empty'.format(lineno))
-            elif OT._is_cypherline(lineno):
+            elif OT._is_cipherline(lineno):
                 self.assertFalse(bool(len(line)),
-                                 'cypher line {0} is empty'.format(lineno))
+                                 'cipher line {0} is empty'.format(lineno))
             else:
                 raise NotImplementedError(lineno)
 
@@ -41,7 +41,7 @@ class TestOneTimePad(unittest.TestCase):
         self.assertTrue(bool(filled))
         for lineno, line in enumerate(filled):
             line = line.strip()
-            if OT._is_cypherline(lineno):
+            if OT._is_cipherline(lineno):
                 self.assertFalse(bool(len(line)),
                                  'line {0} is empty'.format(lineno))
             elif OT._is_txtline(lineno):