diff --git a/src/borg/crypto/keymanager.py b/src/borg/crypto/keymanager.py
index 5f7e5978f..a997c0db6 100644
--- a/src/borg/crypto/keymanager.py
+++ b/src/borg/crypto/keymanager.py
@@ -4,7 +4,7 @@ import textwrap
 from binascii import unhexlify, a2b_base64, b2a_base64
 from hashlib import sha256
 
-from ..helpers import Manifest, NoManifestError, Error, yes, bin_to_hex, open_file_or_stdin
+from ..helpers import Manifest, NoManifestError, Error, yes, bin_to_hex, dash_open
 from ..repository import Repository
 
 from .key import KeyfileKey, KeyfileNotFoundError, KeyBlobStorage, identify_key
@@ -130,7 +130,7 @@ class KeyManager:
     def import_keyfile(self, args):
         file_id = KeyfileKey.FILE_ID
         first_line = file_id + ' ' + bin_to_hex(self.repository.id) + '\n'
-        with open_file_or_stdin(args.path, 'r') as fd:
+        with dash_open(args.path, 'r') as fd:
             file_first_line = fd.read(len(first_line))
             if file_first_line != first_line:
                 if not file_first_line.startswith(file_id):
diff --git a/src/borg/helpers.py b/src/borg/helpers.py
index 31e4e379a..34d7fbd05 100644
--- a/src/borg/helpers.py
+++ b/src/borg/helpers.py
@@ -2178,12 +2178,11 @@ def popen_with_error_handling(cmd_line: str, log_prefix='', **kwargs):
         return
 
 
-def open_file_or_stdin(path, mode):
+def dash_open(path, mode):
+    assert '+' not in mode  # the streams are either r or w, but never both
     if path == '-':
-        if 'b' in mode:
-            return sys.stdin.buffer
-        else:
-            return sys.stdin
+        stream = sys.stdin if 'r' in mode else sys.stdout
+        return stream.buffer if 'b' in mode else stream
     else:
         return open(path, mode)
 
diff --git a/src/borg/testsuite/helpers.py b/src/borg/testsuite/helpers.py
index 9dba4d5e0..2a4160d2c 100644
--- a/src/borg/testsuite/helpers.py
+++ b/src/borg/testsuite/helpers.py
@@ -28,7 +28,7 @@ from ..helpers import swidth_slice
 from ..helpers import chunkit
 from ..helpers import safe_ns, safe_s, SUPPORT_32BIT_PLATFORMS
 from ..helpers import popen_with_error_handling
-from ..helpers import open_file_or_stdin
+from ..helpers import dash_open
 
 from . import BaseTestCase, FakeInputs
 
@@ -945,6 +945,8 @@ class TestPopenWithErrorHandling:
             popen_with_error_handling('', shell=True)
 
 
-def test_open_file_or_stdin():
-    assert open_file_or_stdin('-', 'r') is sys.stdin
-    assert open_file_or_stdin('-', 'rb') is sys.stdin.buffer
+def test_dash_open():
+    assert dash_open('-', 'r') is sys.stdin
+    assert dash_open('-', 'w') is sys.stdout
+    assert dash_open('-', 'rb') is sys.stdin.buffer
+    assert dash_open('-', 'wb') is sys.stdout.buffer