diff --git a/requirements.txt b/requirements.txt
index d12f666..2eacb92 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,3 +7,4 @@ scipy==1.1.0
 pytest==3.5.1
 radon==2.2.0
 pytest-cov==2.5.1
+urllib3>=2.2.2 # not directly required, pinned by Snyk to avoid a vulnerability