diff --git a/acme/setup.py b/acme/setup.py
index 75f889648..85492d9a3 100644
--- a/acme/setup.py
+++ b/acme/setup.py
@@ -17,7 +17,7 @@ install_requires = [
     'PyOpenSSL>=0.13',
     'pyrfc3339',
     'pytz',
-    'requests[security]>=2.20.0',  # DeprecationWarning on Callable in Python3.7
+    'requests[security]>=2.4.1',  # security extras added in 2.4.1
     'requests-toolbelt>=0.3.0',
     'setuptools',
     'six>=1.9.0',  # needed for python_2_unicode_compatible
diff --git a/tools/oldest_constraints.txt b/tools/oldest_constraints.txt
index 6722d7f15..de2b83ad8 100644
--- a/tools/oldest_constraints.txt
+++ b/tools/oldest_constraints.txt
@@ -43,7 +43,7 @@ oauth2client==2.0
 parsedatetime==1.3
 pyparsing==1.5.5
 python-digitalocean==1.11
-requests[security]==2.20.0
+requests[security]==2.4.1
 
 # Ubuntu Xenial constraints
 ConfigArgParse==0.10.0