diff --git a/bincio/serve/server.py b/bincio/serve/server.py
index fba81ce..260cf85 100644
--- a/bincio/serve/server.py
+++ b/bincio/serve/server.py
@@ -1129,6 +1129,7 @@ def _file_suffix(name: str) -> str:
 async def upload_activity(
     files: list[UploadFile] = File(...),
     store_original: bool = Form(False),
+    overwrite: bool = Form(False),
     bincio_session: Optional[str] = Cookie(default=None),
 ) -> StreamingResponse:
     """Accept FIT/GPX/TCX files and/or activities.csv; stream SSE progress while processing.
@@ -1138,9 +1139,9 @@ async def upload_activity(
       - Retroactively update sidecars for existing activities (matched by strava_id)
 
     SSE events:
-      {"type": "progress", "n": N, "total": T, "name": "...", "status": "imported"|"duplicate"|"error"}
+      {"type": "progress", "n": N, "total": T, "name": "...", "status": "imported"|"overwritten"|"duplicate"|"error"}
       {"type": "csv", "updates": N}   -- only when CSV was included
-      {"type": "done", "added": N, "csv_updates": N, "duplicates": N, "errors": N}
+      {"type": "done", "added": N, "csv_updates": N, "duplicates": N, "overwritten": N, "errors": N}
     """
     from bincio.extract.ingest import ingest_parsed
     from bincio.extract.parsers.factory import parse_file
@@ -1182,6 +1183,7 @@ async def upload_activity(
 
     def event_stream():
         added = 0
+        overwritten = 0
         duplicates = 0
         errors = 0
         any_added = False
@@ -1209,19 +1211,51 @@ async def upload_activity(
                 if metadata is not None:
                     metadata.enrich(name, activity)
                 activity_id = make_activity_id(activity)
+                was_overwrite = False
                 if (dd / "activities" / f"{activity_id}.json").exists():
-                    duplicates += 1
-                    yield f"data: {json.dumps({'type': 'progress', 'n': n, 'total': total_files, 'name': name, 'status': 'duplicate'})}\n\n"
-                    continue
+                    if not overwrite:
+                        duplicates += 1
+                        yield f"data: {json.dumps({'type': 'progress', 'n': n, 'total': total_files, 'name': name, 'status': 'duplicate'})}\n\n"
+                        continue
+                    # Overwrite: delete existing files before re-ingesting.
+                    for ext in (".json", ".geojson", ".timeseries.json"):
+                        (dd / "activities" / f"{activity_id}{ext}").unlink(missing_ok=True)
+                    # Remove stale summary from index so ingest_parsed writes a clean one
+                    index_path = dd / "index.json"
+                    if index_path.exists():
+                        idx = json.loads(index_path.read_text(encoding="utf-8"))
+                        idx["activities"] = [a for a in idx.get("activities", []) if a.get("id") != activity_id]
+                        index_path.write_text(json.dumps(idx, indent=2, ensure_ascii=False))
+                    # Remove from dedup hash cache so the new file isn't blocked
+                    cache_path = dd / ".bincio_cache.json"
+                    if cache_path.exists():
+                        try:
+                            cache = json.loads(cache_path.read_text(encoding="utf-8"))
+                            cache.pop(activity_id, None)
+                            cache_path.write_text(json.dumps(cache, ensure_ascii=False))
+                        except Exception:
+                            pass
+                    # Remove merged copies (merge_all will regenerate them after ingest)
+                    merged_acts = dd / "_merged" / "activities"
+                    if merged_acts.exists():
+                        for ext in (".json", ".geojson", ".timeseries.json"):
+                            p = merged_acts / f"{activity_id}{ext}"
+                            if p.exists() or p.is_symlink():
+                                p.unlink(missing_ok=True)
+                    was_overwrite = True
                 ingest_parsed(activity, dd, privacy="public")
                 if store_original:
                     originals_dir = dd / "originals"
                     originals_dir.mkdir(exist_ok=True)
                     staged.rename(originals_dir / name)
                     kept = True
-                added += 1
+                if was_overwrite:
+                    overwritten += 1
+                else:
+                    added += 1
                 any_added = True
-                yield f"data: {json.dumps({'type': 'progress', 'n': n, 'total': total_files, 'name': name, 'status': 'imported'})}\n\n"
+                status = 'overwritten' if was_overwrite else 'imported'
+                yield f"data: {json.dumps({'type': 'progress', 'n': n, 'total': total_files, 'name': name, 'status': status})}\n\n"
             except Exception as exc:
                 errors += 1
                 log.error("upload[%s]: failed to process %s: %s", user.handle, name, exc, exc_info=True)
@@ -1243,7 +1277,7 @@ async def upload_activity(
             if any_added:
                 _trigger_rebuild(user.handle)
 
-        yield f"data: {json.dumps({'type': 'done', 'added': added, 'csv_updates': csv_updates, 'duplicates': duplicates, 'errors': errors})}\n\n"
+        yield f"data: {json.dumps({'type': 'done', 'added': added, 'overwritten': overwritten, 'csv_updates': csv_updates, 'duplicates': duplicates, 'errors': errors})}\n\n"
 
         if job_id:
             _job_finish(job_id)
diff --git a/site/src/layouts/Base.astro b/site/src/layouts/Base.astro
index 531a22e..8b92e23 100644
--- a/site/src/layouts/Base.astro
+++ b/site/src/layouts/Base.astro
@@ -317,6 +317,17 @@ try {
               <span class="text-zinc-600 block mt-0.5">Lets you reprocess if the format changes. See the <a href={`${baseUrl}about/`} class="underline hover:text-zinc-400">About page</a> for details.</span>
             </span>
           </label>
+          <label class="flex items-start gap-2 mt-2 cursor-pointer group">
+            <input
+              id="upload-overwrite"
+              type="checkbox"
+              class="mt-0.5 accent-amber-500 shrink-0"
+            />
+            <span class="text-xs text-zinc-500 group-hover:text-zinc-300 transition-colors leading-snug">
+              Overwrite existing activities
+              <span class="text-zinc-600 block mt-0.5">Re-extract and replace any duplicate found on the server. Use to fix a corrupted or mis-parsed activity.</span>
+            </span>
+          </label>
           <p id="upload-status" class="mt-3 text-xs text-center" style="color: var(--text-5); min-height: 1.25rem"></p>
         </div>
 
@@ -554,6 +565,7 @@ try {
       const input             = document.getElementById('upload-input');
       const label             = document.getElementById('upload-label');
       const keepOriginalChk   = document.getElementById('upload-keep-original');
+      const overwriteChk      = document.getElementById('upload-overwrite');
       const fileStatus        = document.getElementById('upload-status');
       const stravaStatus  = document.getElementById('strava-status');
       const stravaConnect = document.getElementById('strava-connect-area');
@@ -629,6 +641,7 @@ try {
         const fd = new FormData();
         for (const f of files) fd.append('files', f);
         fd.append('store_original', keepOriginalChk?.checked ? 'true' : 'false');
+        fd.append('overwrite', overwriteChk?.checked ? 'true' : 'false');
 
         const xhr = new XMLHttpRequest();
         xhr.open('POST', `${editUrl}/api/upload`);
@@ -636,7 +649,7 @@ try {
         xhr.setRequestHeader('Accept', 'text/event-stream');
 
         let buf = '';
-        let added = 0, dupes = 0, errors = 0, csvUpdates = 0;
+        let added = 0, overwrittenCount = 0, dupes = 0, errors = 0, csvUpdates = 0;
 
         xhr.onprogress = () => {
           const newText = xhr.responseText.slice(buf.length);
@@ -647,23 +660,25 @@ try {
               const ev = JSON.parse(line.slice(6));
               if (ev.type === 'progress') {
                 const pct = Math.round((ev.n / ev.total) * 100);
-                const icon = ev.status === 'imported' ? '↓' : ev.status === 'duplicate' ? '·' : '✗';
+                const icon = ev.status === 'imported' ? '↓' : ev.status === 'overwritten' ? '↺' : ev.status === 'duplicate' ? '·' : '✗';
                 fileStatus.textContent = `${icon} ${ev.n}/${ev.total} (${pct}%) — ${ev.name}`;
                 if (ev.status === 'imported') added++;
+                else if (ev.status === 'overwritten') overwrittenCount++;
                 else if (ev.status === 'duplicate') dupes++;
                 else errors++;
               } else if (ev.type === 'csv') {
                 csvUpdates = ev.updates;
               } else if (ev.type === 'done') {
-                added = ev.added; dupes = ev.duplicates; errors = ev.errors; csvUpdates = ev.csv_updates;
+                added = ev.added; overwrittenCount = ev.overwritten ?? 0; dupes = ev.duplicates; errors = ev.errors; csvUpdates = ev.csv_updates;
                 const parts = [];
                 if (added > 0) parts.push(`${added} added`);
+                if (overwrittenCount > 0) parts.push(`${overwrittenCount} overwritten`);
                 if (csvUpdates > 0) parts.push(`${csvUpdates} updated from CSV`);
                 if (dupes) parts.push(`${dupes} duplicate${dupes > 1 ? 's' : ''}`);
                 if (errors) parts.push(`${errors} failed`);
                 if (parts.length === 0) parts.push('nothing to add');
                 fileStatus.textContent = parts.join(', ');
-                const anyGood = added > 0 || csvUpdates > 0;
+                const anyGood = added > 0 || overwrittenCount > 0 || csvUpdates > 0;
                 fileStatus.style.color = anyGood ? '#4ade80' : '#a1a1aa';
                 if (anyGood) setTimeout(() => window.location.reload(), 1200);
                 else drop.style.pointerEvents = '';