1 files changed, 4 insertions, 0 deletions
diff --git a/src/cryptography/x509.py b/src/cryptography/x509.py
index 668bc2ef..a091cd78 100644
--- a/src/cryptography/x509.py
+++ b/src/cryptography/x509.py
@@ -1472,6 +1472,10 @@ class CertificateSigningRequestBuilder(object):
             extension = Extension(
                 OID_SUBJECT_ALTERNATIVE_NAME, critical, extension
             )
+        elif isinstance(extension, KeyUsage):
+            extension = Extension(
+                OID_KEY_USAGE, critical, extension
+            )
         else:
             raise NotImplementedError('Unsupported X.509 extension.')
         # TODO: This is quadratic in the number of extensions