diff --git a/app/routers/contacts.py b/app/routers/contacts.py
index c6df141..abb5efb 100644
--- a/app/routers/contacts.py
+++ b/app/routers/contacts.py
@@ -193,9 +193,11 @@ async def sync_contacts_from_radio() -> dict:
     count = 0
 
     for public_key, contact_data in contacts.items():
-        await ContactRepository.upsert(
-            Contact.from_radio_dict(public_key, contact_data, on_radio=True)
-        )
+        lower_key = public_key.lower()
+        await ContactRepository.upsert(Contact.from_radio_dict(lower_key, contact_data, on_radio=True))
+        claimed = await MessageRepository.claim_prefix_messages(lower_key)
+        if claimed > 0:
+            logger.info("Claimed %d prefix DM message(s) for contact %s", claimed, public_key[:12])
         count += 1
 
     logger.info("Synced %d contacts from radio", count)
diff --git a/tests/test_contacts_router.py b/tests/test_contacts_router.py
index 62f1496..76c6073 100644
--- a/tests/test_contacts_router.py
+++ b/tests/test_contacts_router.py
@@ -14,7 +14,7 @@ import pytest
 from meshcore import EventType
 
 from app.database import Database
-from app.repository import ContactRepository
+from app.repository import ContactRepository, MessageRepository
 
 # Sample 64-char hex public keys for testing
 KEY_A = "aa" * 32  # aaaa...aa
@@ -301,6 +301,36 @@ class TestSyncContacts:
 
         assert response.status_code == 503
 
+    @pytest.mark.asyncio
+    async def test_sync_claims_prefix_messages(self, test_db, client):
+        """Syncing contacts promotes prefix-stored DM messages to the full key."""
+        await MessageRepository.create(
+            msg_type="PRIV",
+            text="hello from prefix",
+            received_at=1700000000,
+            conversation_key=KEY_A[:12],
+            sender_timestamp=1700000000,
+        )
+
+        mock_mc = MagicMock()
+        mock_result = MagicMock()
+        mock_result.type = EventType.OK
+        mock_result.payload = {KEY_A: {"adv_name": "Alice", "type": 1, "flags": 0}}
+        mock_mc.commands.get_contacts = AsyncMock(return_value=mock_result)
+
+        with patch("app.dependencies.radio_manager") as mock_dep_rm:
+            mock_dep_rm.is_connected = True
+            mock_dep_rm.meshcore = mock_mc
+
+            response = await client.post("/api/contacts/sync")
+
+        assert response.status_code == 200
+        assert response.json()["synced"] == 1
+
+        messages = await MessageRepository.get_all(conversation_key=KEY_A)
+        assert len(messages) == 1
+        assert messages[0].conversation_key == KEY_A.lower()
+
 
 class TestAddRemoveRadio:
     """Test add-to-radio and remove-from-radio endpoints."""