diff --git a/requirements/prod.txt b/requirements/prod.txt
index e7ca09cb8f25..fe7e2f488736 100644
--- a/requirements/prod.txt
+++ b/requirements/prod.txt
@@ -35,9 +35,9 @@ Pillow==4.1.0 \
     --hash=sha256:7b769f1115c6c4a6a567a2e4e8406f0469fb4043b20239778aafbdf3d4ff49f5 \
     --hash=sha256:d3499d67551b3699e5478e80c8132cf60180bb78839ed18fafbff968f858cfeb
 # PyJWT is required by djangorestframework-jwt
-PyJWT==1.4.2 \
-    --hash=sha256:99fe612dbe5f41e07124d9002c118c14f3ee703574ffa9779fee78135b8b94b6 \
-    --hash=sha256:87a831b7a3bfa8351511961469ed0462a769724d4da48a501cb8c96d1e17f570
+PyJWT==1.5.0 \
+    --hash=sha256:ad60a3fb9b393667864ed4b8abc9c3b570747f80bf77a113ead2fbaf0f0cedf3 \
+    --hash=sha256:fd182b728d13f04c289d9b2623d09256d356c9b4a6778018001454a954d7c54b
 SQLAlchemy==0.7.5 \
     --hash=sha256:7e31190a15753694dcb6f4399ce7d02091b0bccf825272d6254e56144debfd18 # pyup: ==0.7.5
 amo-validator==1.10.59 \
diff --git a/src/olympia/api/jwt_auth.py b/src/olympia/api/jwt_auth.py
index 76287d75449a..878041a04f53 100644
--- a/src/olympia/api/jwt_auth.py
+++ b/src/olympia/api/jwt_auth.py
@@ -12,6 +12,9 @@
 
 See https://github.com/GetBlimp/django-rest-framework-jwt/ for more info.
 """
+from calendar import timegm
+from datetime import datetime
+
 from django.conf import settings
 from django.core.exceptions import ObjectDoesNotExist
 
@@ -63,7 +66,10 @@ def jwt_decode_handler(token, get_api_key=APIKey.get_jwt_key):
         'require_iat': True,
         'require_nbf': False,
     }
+
     try:
+        now = timegm(datetime.utcnow().utctimetuple())
+
         payload = jwt.decode(
             token,
             api_key.secret,
@@ -71,6 +77,14 @@ def jwt_decode_handler(token, get_api_key=APIKey.get_jwt_key):
             leeway=api_settings.JWT_LEEWAY,
             algorithms=[api_settings.JWT_ALGORITHM]
         )
+
+        # Verify clock skew for future iat-values pyjwt removed that check in
+        # https://github.com/jpadilla/pyjwt/pull/252/
+        # `verify_iat` is still in options because pyjwt still validates
+        # that `iat` is a proper number.
+        if int(payload['iat']) > (now + api_settings.JWT_LEEWAY):
+            raise jwt.InvalidIssuedAtError(
+                'Issued At claim (iat) cannot be in the future.')
     except jwt.MissingRequiredClaimError, exc:
         log.info(u'Missing required claim during JWT authentication: '
                  u'{e.__class__.__name__}: {e}'.format(e=exc))
diff --git a/src/olympia/api/tests/test_jwt_auth.py b/src/olympia/api/tests/test_jwt_auth.py
index fed8b62ac8dd..0ebf4e0c0b6b 100644
--- a/src/olympia/api/tests/test_jwt_auth.py
+++ b/src/olympia/api/tests/test_jwt_auth.py
@@ -116,7 +116,8 @@ def test_missing_issued_at_time(self):
     def test_invalid_issued_at_time(self):
         api_key = self.create_api_key(self.user)
         payload = self.auth_token_payload(self.user, api_key.key)
-        # Simulate clock skew:
+
+        # Simulate clock skew...
         payload['iat'] = (
             datetime.utcnow() +
             timedelta(seconds=settings.JWT_AUTH['JWT_LEEWAY'] + 10))
@@ -128,6 +129,20 @@ def test_invalid_issued_at_time(self):
         assert ctx.exception.detail.startswith(
             'JWT iat (issued at time) is invalid.')
 
+    def test_invalid_issued_at_time_not_number(self):
+        api_key = self.create_api_key(self.user)
+        payload = self.auth_token_payload(self.user, api_key.key)
+
+        # Simulate clock skew...
+        payload['iat'] = 'thisisnotanumber'
+        token = self.encode_token_payload(payload, api_key.secret)
+
+        with self.assertRaises(AuthenticationFailed) as ctx:
+            jwt_auth.jwt_decode_handler(token)
+
+        assert ctx.exception.detail.startswith(
+            'JWT iat (issued at time) is invalid.')
+
     def test_missing_expiration(self):
         api_key = self.create_api_key(self.user)
         payload = self.auth_token_payload(self.user, api_key.key)
diff --git a/tests/ui/requirements.txt b/tests/ui/requirements.txt
index 22bec606af71..1d2d4be63635 100644
--- a/tests/ui/requirements.txt
+++ b/tests/ui/requirements.txt
@@ -1,5 +1,5 @@
 fxapom==1.10.0
-PyJWT==1.4.2
+PyJWT==1.5.0
 PyPOM==1.1.1
 pytest==3.0.7
 pytest-instafail==0.3.0