diff --git a/bincio/segments/store.py b/bincio/segments/store.py
index 833ec66..98c0988 100644
--- a/bincio/segments/store.py
+++ b/bincio/segments/store.py
@@ -172,10 +172,15 @@ def save_efforts(data_dir: Path, handle: str, segment_id: str, efforts: list[Seg
 
 
 def add_effort(data_dir: Path, handle: str, segment_id: str, effort: SegmentEffort) -> None:
-    """Append an effort, replacing any existing effort with the same activity + start time."""
+    """Append an effort, replacing any existing effort at the same start time.
+
+    Deduplicating by started_at (not activity_id) handles the case where the
+    same ride is stored under two activity IDs (e.g. re-imported with a different
+    source hash), which would otherwise produce two identical-time efforts.
+    """
     efforts = load_efforts(data_dir, handle, segment_id)
-    key = (effort.activity_id, _iso(effort.started_at))
-    efforts = [e for e in efforts if (e.activity_id, _iso(e.started_at)) != key]
+    key = _iso(effort.started_at)
+    efforts = [e for e in efforts if _iso(e.started_at) != key]
     efforts.append(effort)
     efforts.sort(key=lambda e: e.started_at, reverse=True)
     save_efforts(data_dir, handle, segment_id, efforts)