diff --git a/src/log_setup/rotation.py b/src/log_setup/rotation.py
index 4967256..96b7def 100644
--- a/src/log_setup/rotation.py
+++ b/src/log_setup/rotation.py
@@ -288,8 +288,14 @@ def retier(log_dir: str, stem: str, keep_uncompressed: int, keep_compressed: int
     files.sort(key=lambda t: (t[1], t[2]), reverse=True)
 
     keep = keep_uncompressed + keep_compressed
+    present = {p for p, _, _ in files}
     for index, (path, _, _) in enumerate(files):
         if index >= keep:
+            # never delete an intact plain whose only surviving twin is a CORRUPT .gz -
+            # that would leave the corrupt archive as the sole copy (data loss). keep the
+            # plain; a later retier retires it once a clean .gz exists.
+            if not path.endswith(".gz") and (path + ".gz") in present and not _gz_intact(path + ".gz"):
+                continue
             try:
                 os.remove(path)
             except OSError: