diff --git a/server/routes/caldav.js b/server/routes/caldav.js
index 9fbb9e1..f413207 100644
--- a/server/routes/caldav.js
+++ b/server/routes/caldav.js
@@ -210,7 +210,7 @@ async function caldavAuth(req, res, next) {
     }
     // Migrate legacy plaintext token to hashed version
     if (tokenRowLegacy && !tokenRow) {
-      db.run('UPDATE caldav_tokens SET token_hash = ?, token = NULL WHERE id = ?', [tokenHash, matchedToken.id]).catch(() => {});
+      db.run("UPDATE caldav_tokens SET token_hash = ?, token = '' WHERE id = ?", [tokenHash, matchedToken.id]).catch(() => {});
     }
     // Update last_used_at (fire and forget)
     db.run('UPDATE caldav_tokens SET last_used_at = CURRENT_TIMESTAMP WHERE id = ?', [matchedToken.id]).catch(() => {});