diff --git a/lib/db.ts b/lib/db.ts
index 01ad444..cb7464c 100644
--- a/lib/db.ts
+++ b/lib/db.ts
@@ -247,12 +247,17 @@ const SYMBOLS = ['NQ','MNQ','ES','MES','YM','MYM','RTY','M2K','GC','MGC','SI','C
 // from the Instruments page, they just start off.
 const DEFAULT_ENABLED = new Set(['NQ', 'GC', 'CL']);
 
-// Seed instruments table if empty
-const instrCount = (db.prepare('SELECT COUNT(*) as count FROM instruments').get() as { count: number }).count;
-if (instrCount === 0) {
-    const ins = db.prepare('INSERT INTO instruments (symbol, enabled) VALUES (?, ?)');
+// Seed instruments table if empty. Check and insert share one IMMEDIATE
+// transaction: `next build` imports this module from several workers at once,
+// and on a fresh machine they all saw an empty table and raced to insert the
+// same symbols (UNIQUE constraint failed: instruments.symbol). OR IGNORE is
+// the backstop if the lock is ever skipped.
+db.transaction(() => {
+    const instrCount = (db.prepare('SELECT COUNT(*) as count FROM instruments').get() as { count: number }).count;
+    if (instrCount > 0) return;
+    const ins = db.prepare('INSERT OR IGNORE INTO instruments (symbol, enabled) VALUES (?, ?)');
     for (const s of SYMBOLS) ins.run(s, DEFAULT_ENABLED.has(s) ? 1 : 0);
-}
+}).immediate();
 
 export interface InstrumentRow {
     symbol: string;