diff --git a/pungi/ostree/tree.py b/pungi/ostree/tree.py
index f2d2942d..6a9e5e10 100644
--- a/pungi/ostree/tree.py
+++ b/pungi/ostree/tree.py
@@ -48,13 +48,20 @@ class Tree(OSTree):
             cmd.append('--force-nocache')
         cmd.append(self.treefile)
 
-        shortcuts.run(cmd, show_cmd=True, stdout=True, logfile=log_file)
+        shortcuts.run(
+            cmd, show_cmd=True, stdout=True, logfile=log_file, universal_newlines=True
+        )
 
     def _update_summary(self):
         """Update summary metadata"""
         log_file = make_log_file(self.logdir, 'ostree-summary')
-        shortcuts.run(['ostree', 'summary', '-u', '--repo=%s' % self.repo],
-                      show_cmd=True, stdout=True, logfile=log_file)
+        shortcuts.run(
+            ['ostree', 'summary', '-u', '--repo=%s' % self.repo],
+            show_cmd=True,
+            stdout=True,
+            logfile=log_file,
+            universal_newlines=True,
+        )
 
     def _update_ref(self):
         """
diff --git a/tests/test_ostree_script.py b/tests/test_ostree_script.py
index 9aa569a3..9490d935 100644
--- a/tests/test_ostree_script.py
+++ b/tests/test_ostree_script.py
@@ -54,6 +54,7 @@ class OstreeTreeScriptTest(helpers.PungiTestCase):
                     logfile=self.topdir + "/logs/Atomic/create-ostree-repo.log",
                     show_cmd=True,
                     stdout=True,
+                    universal_newlines=True,
                 )
             ] + extra_calls
         )
@@ -113,6 +114,7 @@ class OstreeTreeScriptTest(helpers.PungiTestCase):
                     logfile=self.topdir + "/logs/Atomic/ostree-summary.log",
                     show_cmd=True,
                     stdout=True,
+                    universal_newlines=True,
                 )
             ]
         )