diff --git a/CHANGELOG.md b/CHANGELOG.md
index a7e71f265..56faf8efb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,14 @@
 
 [1]: https://pypi.org/project/google-auth/#history
 
+### [1.20.1](https://www.github.com/googleapis/google-auth-library-python/compare/v1.20.0...v1.20.1) (2020-08-06)
+
+
+### Bug Fixes
+
+* reduce refresh clock skew to 10 seconds ([#581](https://www.github.com/googleapis/google-auth-library-python/issues/581)) ([42321ba](https://www.github.com/googleapis/google-auth-library-python/commit/42321bafd38a8bd806f4d01bfa0eda3b5a961667))
+* set Content-Type header in the request to signBlob API to avoid Invalid JSON payload error ([#439](https://www.github.com/googleapis/google-auth-library-python/issues/439)) ([20f82e2](https://www.github.com/googleapis/google-auth-library-python/commit/20f82e22b7e8c6c7fdd29e08eaf7b4cf2abdcf37))
+
 ## [1.20.0](https://www.github.com/googleapis/google-auth-library-python/compare/v1.19.2...v1.20.0) (2020-07-23)
 
 
diff --git a/google/auth/_helpers.py b/google/auth/_helpers.py
index ecb88ffda..21c987a73 100644
--- a/google/auth/_helpers.py
+++ b/google/auth/_helpers.py
@@ -22,7 +22,7 @@
 from six.moves import urllib
 
 
-CLOCK_SKEW_SECS = 300  # 5 minutes in seconds
+CLOCK_SKEW_SECS = 10  # 10 seconds
 CLOCK_SKEW = datetime.timedelta(seconds=CLOCK_SKEW_SECS)
 
 
diff --git a/google/auth/iam.py b/google/auth/iam.py
index bd0500457..d83b25180 100644
--- a/google/auth/iam.py
+++ b/google/auth/iam.py
@@ -69,7 +69,7 @@ def _make_signing_request(self, message):
 
         method = "POST"
         url = _SIGN_BLOB_URI.format(self._service_account_email)
-        headers = {}
+        headers = {"Content-Type": "application/json"}
         body = json.dumps(
             {"bytesToSign": base64.b64encode(message).decode("utf-8")}
         ).encode("utf-8")
diff --git a/setup.py b/setup.py
index 5b192b10a..cfa7b0a85 100644
--- a/setup.py
+++ b/setup.py
@@ -33,7 +33,7 @@
 with io.open("README.rst", "r") as fh:
     long_description = fh.read()
 
-version = "1.20.0"
+version = "1.20.1"
 
 setup(
     name="google-auth",
diff --git a/tests/test_iam.py b/tests/test_iam.py
index 4367fe7a8..cb2c26f73 100644
--- a/tests/test_iam.py
+++ b/tests/test_iam.py
@@ -89,6 +89,8 @@ def test_sign_bytes(self):
         returned_signature = signer.sign("123")
 
         assert returned_signature == signature
+        kwargs = request.call_args.kwargs
+        assert kwargs["headers"]["Content-Type"] == "application/json"
 
     def test_sign_bytes_failure(self):
         request = make_request(http_client.UNAUTHORIZED)