Typo fix
diff --git a/cryptography/hazmat/backends/commoncrypto/backend.py b/cryptography/hazmat/backends/commoncrypto/backend.py
index ebb834c..4e70cab 100644
--- a/cryptography/hazmat/backends/commoncrypto/backend.py
+++ b/cryptography/hazmat/backends/commoncrypto/backend.py
@@ -200,8 +200,8 @@
             )
         else:
             raise InternalError(
-                "The backend returned an unkown error, consider filing a bug. "
-                "Code: {0}.".format(response)
+                "The backend returned an unknown error, consider filing a bug."
+                " Code: {0}.".format(response)
             )