diff --git a/rfc7539/aead.py b/rfc7539/aead.py
index e46d9b6..37169c0 100644
--- a/rfc7539/aead.py
+++ b/rfc7539/aead.py
@@ -27,9 +27,16 @@ def _len_bytes(n):
     return slen
 
 
+def _pad16(x):
+    if len(x) % 16 == 0:
+        return b''
+    else:
+        return b'\x00' * (16 - (len(x) % 16))
+
+
 def _tag_data(aad, ciphertext):
-    tag_data = aad + b'\x00' * (16 - (len(aad) % 16))
-    tag_data += ciphertext + b'\x00' * (16 - (len(ciphertext) % 16))
+    tag_data = aad + _pad16(aad)
+    tag_data += ciphertext + _pad16(ciphertext)
     tag_data += _len_bytes(len(aad))
     tag_data += _len_bytes(len(ciphertext))
     return tag_data
diff --git a/setup.py b/setup.py
index 8049d90..3b76bdd 100644
--- a/setup.py
+++ b/setup.py
@@ -32,7 +32,7 @@ def run(self):
 
 setup(
     name='rfc7539',
-    version='1.1.0',
+    version='1.2.1',
     author='Anton Kueltz',
     author_email='kueltz.anton@gmail.com',
     license='GNU General Public License v3 (GPLv3)',