diff --git a/src/borg/helpers/errors.py b/src/borg/helpers/errors.py
index 0aca4729..931d6daf 100644
--- a/src/borg/helpers/errors.py
+++ b/src/borg/helpers/errors.py
@@ -1,3 +1,4 @@
+import errno
 import os
 
 from ..constants import *  # NOQA
@@ -119,6 +120,27 @@ class BackupOSWarning(BorgWarning):
 
     exit_mcode = 104
 
+    @property
+    def exit_code(self):
+        if not modern_ec:
+            return EXIT_WARNING
+        exc = self.args[1]
+        assert isinstance(exc, BackupOSError)
+        if exc.errno in (errno.EPERM, errno.EACCES):
+            return PermissionWarning.exit_mcode
+        elif exc.errno in (errno.EIO,):
+            return IOWarning.exit_mcode
+        else:
+            return self.exit_mcode
+
+
+class PermissionWarning(BorgWarning):
+    exit_mcode = 105
+
+
+class IOWarning(BorgWarning):
+    exit_mcode = 106
+
 
 class BackupError(Exception):
     """