cleanup context after finalizing
diff --git a/cryptography/hazmat/bindings/openssl/backend.py b/cryptography/hazmat/bindings/openssl/backend.py
index 300495c..db5a9e1 100644
--- a/cryptography/hazmat/bindings/openssl/backend.py
+++ b/cryptography/hazmat/bindings/openssl/backend.py
@@ -287,6 +287,7 @@
buflen[0] = digest_size
res = self._backend.lib.HMAC_Final(ctx, buf, buflen)
assert res != 0
+ self._backend.lib.HMAC_CTX_cleanup(ctx)
return self._backend.ffi.buffer(buf)[:digest_size]
def copy_ctx(self, ctx):