diff --git a/src/uproot/_dask.py b/src/uproot/_dask.py
index e2f72053c..b671aa955 100644
--- a/src/uproot/_dask.py
+++ b/src/uproot/_dask.py
@@ -762,7 +762,7 @@ def __call__(self, i_start_stop):
             dask_awkward = uproot.extras.dask_awkward()
 
             if all_common_keys != set(self.rendered_form.columns()):
-                actual_form = self.rendered_form.select_columns(all_common_keys)
+                actual_form = self.rendered_form.select_columns(list(all_common_keys))
             else:
                 actual_form = self.rendered_form
 
@@ -936,7 +936,7 @@ def __call__(self, file_path_object_path_istep_nsteps_ischunk):
             dask_awkward = uproot.extras.dask_awkward()
 
             if all_common_keys != set(self.rendered_form.columns()):
-                actual_form = self.rendered_form.select_columns(all_common_keys)
+                actual_form = self.rendered_form.select_columns(list(all_common_keys))
             else:
                 actual_form = self.rendered_form