diff --git a/tests/compute_engine/test_credentials.py b/tests/compute_engine/test_credentials.py
index 98def0f..363dc9d 100644
--- a/tests/compute_engine/test_credentials.py
+++ b/tests/compute_engine/test_credentials.py
@@ -354,11 +354,11 @@
         signature = base64.b64encode(b"some-signature").decode("utf-8")
         responses.add(
             responses.POST,
-            "https://iam.googleapis.com/v1/projects/-/serviceAccounts/"
-            "service-account@example.com:signBlob?alt=json",
+            "https://iamcredentials.googleapis.com/v1/projects/-/"
+            "serviceAccounts/service-account@example.com:signBlob?alt=json",
             status=200,
             content_type="application/json",
-            json={"keyId": "some-key-id", "signature": signature},
+            json={"keyId": "some-key-id", "signedBlob": signature},
         )
 
         id_token = "{}.{}.{}".format(
diff --git a/tests/test_iam.py b/tests/test_iam.py
index c98a138..ea7d08a 100644
--- a/tests/test_iam.py
+++ b/tests/test_iam.py
@@ -78,7 +78,7 @@
     def test_sign_bytes(self):
         signature = b"DEADBEEF"
         encoded_signature = base64.b64encode(signature).decode("utf-8")
-        request = make_request(http_client.OK, data={"signature": encoded_signature})
+        request = make_request(http_client.OK, data={"signedBlob": encoded_signature})
         credentials = make_credentials()
 
         signer = iam.Signer(request, credentials, mock.sentinel.service_account_email)