diff --git a/app/routes/teller.py b/app/routes/teller.py
index 0cb95c8..efa84ee 100644
--- a/app/routes/teller.py
+++ b/app/routes/teller.py
@@ -271,12 +271,48 @@ def webhook():
     Does NOT auto-import — user must confirm via the UI.
     """
     # Verify Teller webhook signature
+    # Header format: Teller-Signature: t=<timestamp>,v1=<sig1>,v1=<sig2>
+    # Signed message: <timestamp>.<raw_body>
     signing_secret = current_app.config.get('TELLER_WEBHOOK_SECRET', '')
     if signing_secret:
         sig_header = request.headers.get('Teller-Signature', '')
         body = request.get_data()
-        expected = hmac.new(signing_secret.encode(), body, hashlib.sha256).hexdigest()
-        if not hmac.compare_digest(f'sha256={expected}', sig_header):
+
+        if not sig_header:
+            log.warning('[teller] missing Teller-Signature header')
+            return jsonify({'error': 'Missing signature'}), 401
+
+        # Parse header: t=<timestamp>,v1=<sig>,v1=<sig2>...
+        parts = dict(
+            (p.split('=', 1) if '=' in p else (p, ''))
+            for p in sig_header.split(',')
+        )
+        timestamp = parts.get('t', '')
+        # Collect all v1 signatures (may be multiple during key rotation)
+        signatures = [v for k, v in
+                      [p.split('=', 1) for p in sig_header.split(',') if p.startswith('v1=')]
+                      ]
+
+        if not timestamp or not signatures:
+            log.warning('[teller] malformed Teller-Signature header')
+            return jsonify({'error': 'Invalid signature'}), 401
+
+        # Reject replays older than 5 minutes
+        import time
+        try:
+            if abs(time.time() - int(timestamp)) > 300:
+                log.warning('[teller] webhook replay attack detected')
+                return jsonify({'error': 'Timestamp too old'}), 401
+        except ValueError:
+            pass
+
+        # signed_message = timestamp + "." + raw_body
+        signed_message = f'{timestamp}.'.encode() + body
+        expected = hmac.new(
+            signing_secret.encode(), signed_message, hashlib.sha256
+        ).hexdigest()
+
+        if not any(hmac.compare_digest(expected, sig) for sig in signatures):
             log.warning('[teller] webhook signature mismatch')
             return jsonify({'error': 'Invalid signature'}), 401