diff --git a/cryptography/hazmat/primitives/hmac.py b/cryptography/hazmat/primitives/hmac.py
index 2bd8e4d..618bccc 100644
--- a/cryptography/hazmat/primitives/hmac.py
+++ b/cryptography/hazmat/primitives/hmac.py
@@ -47,7 +47,7 @@
         return HMAC(
             self._key,
             self.algorithm,
-            self._backend,
+            backend=self._backend,
             ctx=self._ctx.copy()
         )