diff --git a/requirements.txt b/requirements.txt
index b2e00d610..5485652c3 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -15,6 +15,7 @@
 #       ignored when building a PIP Wheel.
 ##############################################################################
 blinker==1.4
+jaraco.functools==2.0.0
 cheroot==8.2.1
 Flask==1.0.2
 Werkzeug>=0.15.0