diff --git a/requirements_optional.txt b/requirements_optional.txt
index df6b3b387e..8bbf0a6809 100644
--- a/requirements_optional.txt
+++ b/requirements_optional.txt
@@ -1,3 +1,3 @@
-pillow>4.0.0
+pillow>4.0.0,<10.0.0
 cairosvg>=2.2.0
 cryptography>=2.0.0,<4