diff --git a/src/borg/testsuite/archiver.py b/src/borg/testsuite/archiver.py
index 5b1eedeea..52f069596 100644
--- a/src/borg/testsuite/archiver.py
+++ b/src/borg/testsuite/archiver.py
@@ -19,7 +19,7 @@ from configparser import ConfigParser
 from datetime import datetime
 from datetime import timedelta
 from hashlib import sha256
-from io import StringIO
+from io import BytesIO, StringIO
 from unittest.mock import patch
 
 import msgpack
@@ -61,7 +61,7 @@ from . import key
 src_dir = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
 
 
-def exec_cmd(*args, archiver=None, fork=False, exe=None, input=b'', **kw):
+def exec_cmd(*args, archiver=None, fork=False, exe=None, input=b'', binary_output=False, **kw):
     if fork:
         try:
             if exe is None:
@@ -78,12 +78,18 @@ def exec_cmd(*args, archiver=None, fork=False, exe=None, input=b'', **kw):
         except SystemExit as e:  # possibly raised by argparse
             output = ''
             ret = e.code
-        return ret, os.fsdecode(output)
+        if binary_output:
+            return ret, output
+        else:
+            return ret, os.fsdecode(output)
     else:
         stdin, stdout, stderr = sys.stdin, sys.stdout, sys.stderr
         try:
             sys.stdin = StringIO(input.decode())
-            sys.stdout = sys.stderr = output = StringIO()
+            sys.stdin.buffer = BytesIO(input)
+            output = BytesIO()
+            # Always use utf-8 here, to simply .decode() below
+            output_text = sys.stdout = sys.stderr = io.TextIOWrapper(output, encoding='utf-8')
             if archiver is None:
                 archiver = Archiver()
             archiver.prerun_checks = lambda *args: None
@@ -95,9 +101,11 @@ def exec_cmd(*args, archiver=None, fork=False, exe=None, input=b'', **kw):
                 # actions that abort early (eg. --help) where given. Catch this and return
                 # the error code as-if we invoked a Borg binary.
             except SystemExit as e:
-                return e.code, output.getvalue()
+                output_text.flush()
+                return e.code, output.getvalue() if binary_output else output.getvalue().decode()
             ret = archiver.run(args)
-            return ret, output.getvalue()
+            output_text.flush()
+            return ret, output.getvalue() if binary_output else output.getvalue().decode()
         finally:
             sys.stdin, sys.stdout, sys.stderr = stdin, stdout, stderr
 
@@ -927,6 +935,18 @@ class ArchiverTestCase(ArchiverTestCaseBase):
         os.mkdir('input/cache3')
         os.link('input/cache1/%s' % CACHE_TAG_NAME, 'input/cache3/%s' % CACHE_TAG_NAME)
 
+    def test_create_stdin(self):
+        self.cmd('init', '--encryption=repokey', self.repository_location)
+        input_data = b'\x00foo\n\nbar\n   \n'
+        self.cmd('create', self.repository_location + '::test', '-', input=input_data)
+        item = json.loads(self.cmd('list', '--json-lines', self.repository_location + '::test'))
+        assert item['uid'] == 0
+        assert item['gid'] == 0
+        assert item['size'] == len(input_data)
+        assert item['path'] == 'stdin'
+        extracted_data = self.cmd('extract', '--stdout', self.repository_location + '::test', binary_output=True)
+        assert extracted_data == input_data
+
     def test_create_without_root(self):
         """test create without a root"""
         self.cmd('init', '--encryption=repokey', self.repository_location)