called -> used
diff --git a/cryptography/hazmat/primitives/kdf/pbkdf2.py b/cryptography/hazmat/primitives/kdf/pbkdf2.py
index 2c8dd54..c08e7d9 100644
--- a/cryptography/hazmat/primitives/kdf/pbkdf2.py
+++ b/cryptography/hazmat/primitives/kdf/pbkdf2.py
@@ -44,7 +44,7 @@
 
     def derive(self, key_material):
         if self._used:
-            raise AlreadyFinalized("PBKDF2 instances can only be called once")
+            raise AlreadyFinalized("PBKDF2 instances can only be used once")
         self._used = True
 
         if isinstance(key_material, six.text_type):