diff --git a/requirements.txt b/requirements.txt
index 4e9b659b0..d8c98876a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -13,3 +13,4 @@ ufoLib2==0.14.0
 pyobjc==9.0; sys_platform == "darwin"
 freetype-py==2.3.0
 uharfbuzz==0.32.0
+glyphsLib==6.2.1 # this is only required to run Tests/varLib/interpolatable_test.py