diff --git a/python/requirements/CI-tests-conda/requirements.txt b/python/requirements/CI-tests-conda/requirements.txt
index 1b50515ce0..86b23b1b33 100644
--- a/python/requirements/CI-tests-conda/requirements.txt
+++ b/python/requirements/CI-tests-conda/requirements.txt
@@ -1,3 +1,4 @@
 msprime==1.3.2
 tszip==0.2.3
 h5py==3.11.0
+zarr<3