diff --git a/src/borg/repository.py b/src/borg/repository.py
index c08576099..66ecf20a8 100644
--- a/src/borg/repository.py
+++ b/src/borg/repository.py
@@ -1393,8 +1393,14 @@ def recover_segment(self, segment, filename):
             del self.fds[segment]
         backup_filename = filename + '.beforerecover'
         os.rename(filename, backup_filename)
+        if os.path.getsize(backup_filename) < MAGIC_LEN + self.header_fmt.size:
+            # this is either a zero-byte file (which would crash mmap() below) or otherwise
+            # just too small to be a valid non-empty segment file, so do a shortcut here:
+            with open(filename, 'wb') as fd:
+                fd.write(MAGIC)
+            return
         with open(backup_filename, 'rb') as backup_fd:
-            # note: file must not be 0 size (windows can't create 0 size mapping)
+            # note: file must not be 0 size or mmap() will crash.
             with mmap.mmap(backup_fd.fileno(), 0, access=mmap.ACCESS_READ) as mm:
                 # memoryview context manager is problematic, see https://bugs.python.org/issue35686
                 data = memoryview(mm)