diff --git a/requirements/common.txt b/requirements/common.txt
index 6e377867e8..73fef04f35 100644
--- a/requirements/common.txt
+++ b/requirements/common.txt
@@ -101,6 +101,9 @@ pycrypto==2.6.1
 # Needed for memcached usage
 pylibmc==1.5.2
 
+# Needed for zerver/tests/test_timestamp.py
+python-dateutil==2.6.1
+
 # Needed for timezone work
 pytz==2017.2
 
diff --git a/requirements/dev_lock.txt b/requirements/dev_lock.txt
index eabb5c3970..f7d35850a4 100644
--- a/requirements/dev_lock.txt
+++ b/requirements/dev_lock.txt
@@ -106,7 +106,7 @@ pyjwt==1.5.2
 pyldap==2.4.37
 pylibmc==1.5.2
 pyopenssl==17.0.0         # via ndg-httpsclient, scrapy, service-identity
-python-dateutil==2.6.1    # via arrow, botocore, moto
+python-dateutil==2.6.1
 python-gcm==0.4
 python-twitter==3.3
 python3-openid==3.1.0     # via social-auth-core
diff --git a/requirements/prod_lock.txt b/requirements/prod_lock.txt
index 8037ddd7be..843456b81d 100644
--- a/requirements/prod_lock.txt
+++ b/requirements/prod_lock.txt
@@ -74,6 +74,7 @@ pyjwt==1.5.2
 pyldap==2.4.37
 pylibmc==1.5.2
 pyopenssl==17.2.0         # via ndg-httpsclient
+python-dateutil==2.6.1
 python-gcm==0.4
 python-twitter==3.3
 python3-openid==3.1.0     # via social-auth-core