diff --git a/cryptography/exceptions.py b/cryptography/exceptions.py
index 3ccfaf5..c14763f 100644
--- a/cryptography/exceptions.py
+++ b/cryptography/exceptions.py
@@ -22,7 +22,7 @@
     UNSUPPORTED_MGF = object()
     UNSUPPORTED_PUBLIC_KEY_ALGORITHM = object()
     UNSUPPORTED_ELLIPTIC_CURVE = object()
-    UNSUPPORTED_KEY_FORMAT = object()
+    UNSUPPORTED_SERIALIZATION = object()
 
 
 class UnsupportedAlgorithm(Exception):
diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
index c06d243..6182f5c 100644
--- a/cryptography/hazmat/backends/multibackend.py
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -312,6 +312,6 @@
                 continue
 
         raise UnsupportedAlgorithm(
-            "This backend does not support this key format.",
-            _Reasons.UNSUPPORTED_KEY_FORMAT
+            "This backend does not support this key serialization.",
+            _Reasons.UNSUPPORTED_SERIALIZATION
         )
diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
index 1979563..3be8371 100644
--- a/tests/hazmat/backends/test_multibackend.py
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -484,5 +484,5 @@
         backend.load_pkcs8_pem_private_key(b"keydata", None)
 
         backend = MultiBackend([])
-        with raises_unsupported_algorithm(_Reasons.UNSUPPORTED_KEY_FORMAT):
+        with raises_unsupported_algorithm(_Reasons.UNSUPPORTED_SERIALIZATION):
             backend.load_pkcs8_pem_private_key(b"keydata", None)