diff --git a/setup.py b/setup.py
index e2a3b3e1121522f4686eb515ef8f971cef9aeff0..ac8d15dbbdfc0c48f6e71e087c95c2c4418e0f92 100644
--- a/setup.py
+++ b/setup.py
@@ -97,6 +97,7 @@ setup(
         "gwpy",
         "gwosc",
         "matplotlib",
+        "astropy<4.2",
         "numpy",
         "tqdm",
         "corner",