diff --git a/requirements.txt b/requirements.txt
index 9e410a6..2e3ecf8 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -10,3 +10,4 @@ numpydoc>=0.6.0
 sphinx>=1.4.1
 sphinx_rtd_theme>=0.2.0
 cython>=0.29
+fonttools>=4.61.0 # not directly required, pinned by Snyk to avoid a vulnerability