diff --git a/tox.ini b/tox.ini
index 5a33eef..bc842f8 100644
--- a/tox.ini
+++ b/tox.ini
@@ -39,6 +39,7 @@ deps =
     oldestdeps: numpy==1.20.*
     oldestdeps: scipy==1.6.*
     oldestdeps: astropy==5.0.*
+    oldestdeps: attrs < 24.1.0  # ASDF_LT_3_4
     oldestdeps: asdf==2.14.*
     oldestdeps: synphot==1.1.*