Add load_rsa_numbers support to MultiBackend.
diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
index b4cb688..5acec33 100644
--- a/cryptography/hazmat/backends/multibackend.py
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -178,6 +178,13 @@
         raise UnsupportedAlgorithm("RSA is not supported by the backend.",
                                    _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM)
 
+    def load_rsa_numbers(self, numbers):
+        for b in self._filtered_backends(RSABackend):
+            return b.load_rsa_numbers(numbers)
+
+        raise UnsupportedAlgorithm("RSA is not supported by the backend",
+                                   _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM)
+
     def generate_dsa_parameters(self, key_size):
         for b in self._filtered_backends(DSABackend):
             return b.generate_dsa_parameters(key_size)
diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
index 3fa364e..d4c89be 100644
--- a/tests/hazmat/backends/test_multibackend.py
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -23,7 +23,7 @@
 )
 from cryptography.hazmat.backends.multibackend import MultiBackend
 from cryptography.hazmat.primitives import cmac, hashes, hmac
-from cryptography.hazmat.primitives.asymmetric import padding
+from cryptography.hazmat.primitives.asymmetric import padding, rsa
 from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
 
 from ...utils import raises_unsupported_algorithm
@@ -111,6 +111,8 @@
         pass
 
     def encrypt_rsa(self, public_key, plaintext, padding):
+
+    def load_rsa_numbers(self, numbers):
         pass
 
 
@@ -236,6 +238,8 @@
 
         backend.decrypt_rsa("private_key", "encrypted", padding.PKCS1v15())
 
+        backend.load_rsa_numbers(rsa.RSAPublicNumbers(e=3, n=1))
+
         backend = MultiBackend([])
         with raises_unsupported_algorithm(
             _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM
@@ -279,6 +283,11 @@
         ):
             backend.decrypt_rsa("private_key", "encrypted", padding.PKCS1v15())
 
+        with raises_unsupported_algorithm(
+            _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM
+        ):
+            backend.load_rsa_numbers(rsa.RSAPublicNumbers(e=3, n=1))
+
     def test_dsa(self):
         backend = MultiBackend([
             DummyDSABackend()