1 files changed, 6 insertions, 0 deletions
diff --git a/cryptography/primitives/block/ciphers.py b/cryptography/primitives/block/ciphers.py
index f40fc2a1..2bf936ee 100644
--- a/cryptography/primitives/block/ciphers.py
+++ b/cryptography/primitives/block/ciphers.py
@@ -14,11 +14,17 @@
 
 class AES(object):
     name = "AES"
+    key_sizes = {128, 192, 256}
 
     def __init__(self, key):
         super(AES, self).__init__()
         self.key = key
 
+        if self.key_size not in self.key_sizes:
+            raise ValueError("Invalid key size (%s) for %s".format(
+                self.key_size, self.name
+            ))
+
     @property
     def key_size(self):
         return len(self.key) * 8