diff --git a/tox.ini b/tox.ini
index ddd009b1..cf1f51f1 100644
--- a/tox.ini
+++ b/tox.ini
@@ -16,7 +16,7 @@ deps=
     cov: pytest-astropy
     cov: pytest-cov
     syn: synphot
-    legacy: numpy==1.20.0
+    legacy: oldest-supported-numpy
     legacy: astropy==5.1.0
     legacy: scipy==1.10.1
     latest: -rrequirements.txt