diff --git a/requirements.txt b/requirements.txt
index 1e92f17e..b1baadd7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -21,5 +21,5 @@ cardboardlint==1.3.0
 pylint==2.5.3
 gdown
 umap-learn
-cython
+cython==0.29.20 # > 0.29.20 breaks pyworld installation with the min numpy req of Tensorflow 2.4.1
 pyyaml
\ No newline at end of file