diff --git a/scripts/combo-layer b/scripts/combo-layer
index b90bfc8800..4a210fba63 100755
--- a/scripts/combo-layer
+++ b/scripts/combo-layer
@@ -329,7 +329,7 @@ def action_init(conf, args):
                         # one. The commit should be in both repos with
                         # the same tree, but better check here.
                         tree = runcmd('git show -s --pretty=format:%%T %s' % rev).strip()
-                        with tempfile.NamedTemporaryFile() as editor:
+                        with tempfile.NamedTemporaryFile(mode='wt') as editor:
                             editor.write('''cat >$1 <<EOF
 tree %s
 author %s
@@ -353,7 +353,7 @@ EOF
                 # Optional: rewrite history to change commit messages or to move files.
                 if 'hook' in repo or dest_dir != ".":
                     filter_branch = ['git', 'filter-branch', '--force']
-                    with tempfile.NamedTemporaryFile() as hookwrapper:
+                    with tempfile.NamedTemporaryFile(mode='wt') as hookwrapper:
                         if 'hook' in repo:
                             # Create a shell script wrapper around the original hook that
                             # can be used by git filter-branch. Hook may or may not have
@@ -1137,7 +1137,7 @@ def update_with_history(conf, components, revisions, repos):
             if hook:
                 # Need to turn the verbatim commit message into something resembling a patch header
                 # for the hook.
-                with tempfile.NamedTemporaryFile(delete=False) as patch:
+                with tempfile.NamedTemporaryFile(mode='wt', delete=False) as patch:
                     patch.write('Subject: [PATCH] ')
                     patch.write(body)
                     patch.write('\n---\n')