diff --git a/jdaviz/configs/default/plugins/model_fitting/tests/test_blackbody.py b/jdaviz/configs/default/plugins/model_fitting/tests/test_blackbody.py
index bacc6eb4fc..27f8a7432e 100644
--- a/jdaviz/configs/default/plugins/model_fitting/tests/test_blackbody.py
+++ b/jdaviz/configs/default/plugins/model_fitting/tests/test_blackbody.py
@@ -1,4 +1,5 @@
 # Licensed under a 3-clause BSD style license - see LICENSE.rst
+# copied and modified from astropy: https://github.com/astropy/astropy/pull/12304
 """Tests for physical functions."""
 # pylint: disable=no-member, invalid-name
 import pytest
diff --git a/jdaviz/models/physical_models.py b/jdaviz/models/physical_models.py
index 37e33574cb..de4dd78843 100644
--- a/jdaviz/models/physical_models.py
+++ b/jdaviz/models/physical_models.py
@@ -1,4 +1,5 @@
 # Licensed under a 3-clause BSD style license - see LICENSE.rst
+# copied and modified from astropy: https://github.com/astropy/astropy/pull/12304
 """
 Models that have physical origins.
 """
@@ -269,7 +270,11 @@ def output_units(self, unit):
                 # let's provide some convenience for passing these as strings
                 unit = self._native_output_units.get(unit)
             else:
-                unit = u.Unit(unit)
+                try:
+                    unit = u.Unit(unit)
+                except ValueError:
+                    # then the string wasn't a valid unit, we'll allow the error below to be raised
+                    pass
 
         if unit is None:
             pass