diff --git a/jose/jwk.py b/jose/jwk.py
index 87f30b41..7a7bc45e 100644
--- a/jose/jwk.py
+++ b/jose/jwk.py
@@ -53,11 +53,11 @@ def construct(key_data, algorithm=None):
         algorithm = key_data.get('alg', None)
 
     if not algorithm:
-        raise JWKError('Unable to find a algorithm for key: %s' % key_data)
+        raise JWKError('Unable to find an algorithm for key: %s' % key_data)
 
     key_class = get_key(algorithm)
     if not key_class:
-        raise JWKError('Unable to find a algorithm for key: %s' % key_data)
+        raise JWKError('Unable to find an algorithm for key: %s' % key_data)
     return key_class(key_data, algorithm)