diff --git a/lib/db.js b/lib/db.js
index f1b01a3..4a3ef4a 100644
--- a/lib/db.js
+++ b/lib/db.js
@@ -21,7 +21,12 @@ function query(text, params) {
 }
 
 // Run a function inside a transaction, passing it a dedicated client.
-async function transaction(fn) {
+// Postgres breaks a deadlock by killing one of the transactions. The victim
+// rolled back and changed nothing, so running it again is safe — and usually
+// works, because the transaction it collided with has since finished.
+const RETRY_CODES = new Set(['40P01', '40001']); // deadlock_detected, serialization_failure
+
+async function transaction(fn, attempt = 0) {
   const client = await pool.connect();
   try {
     await client.query('BEGIN');
@@ -29,11 +34,14 @@ async function transaction(fn) {
     await client.query('COMMIT');
     return result;
   } catch (err) {
-    await client.query('ROLLBACK');
-    throw err;
+    await client.query('ROLLBACK').catch(() => {}); // the connection may be gone
+    if (!RETRY_CODES.has(err.code) || attempt >= 3) throw err;
+    console.warn(`Database ${err.code}, retrying the transaction (attempt ${attempt + 2}).`);
   } finally {
-    client.release();
+    client.release(); // before the pause below, so a retry doesn't hold a connection
   }
+  await new Promise((r) => setTimeout(r, 50 * (attempt + 1) ** 2));
+  return transaction(fn, attempt + 1);
 }
 
 module.exports = { pool, query, transaction, init };
diff --git a/lib/store.js b/lib/store.js
index 5939c0f..5605e55 100644
--- a/lib/store.js
+++ b/lib/store.js
@@ -301,11 +301,25 @@ async function insertFile(client, modelId, file) {
 }
 
 // ---------------------------------------------------------------- tags
+// Always tag in the same order. Two transactions touching the same tags in
+// opposite orders each hold a row the other wants, which Postgres resolves by
+// killing one of them ("deadlock detected").
+const tagOrder = (names) => [...new Set((names || []).map((n) => String(n).trim()).filter(Boolean))].sort();
+
+// The tag's id, creating it if it's new. Deliberately not ON CONFLICT DO UPDATE:
+// that rewrites the row and so write-locks it for the rest of the transaction,
+// even though the name never changes — which is what made tagging deadlock.
 async function tagId(client, name) {
-  const { rows } = await client.query(
-    `INSERT INTO tags (name) VALUES ($1)
-     ON CONFLICT (name) DO UPDATE SET name = EXCLUDED.name RETURNING id`, [name]);
-  return rows[0].id;
+  for (let attempt = 0; attempt < 3; attempt++) {
+    const { rows: found } = await client.query('SELECT id FROM tags WHERE name = $1', [name]);
+    if (found.length) return found[0].id;
+    const { rows } = await client.query(
+      'INSERT INTO tags (name) VALUES ($1) ON CONFLICT (name) DO NOTHING RETURNING id', [name]);
+    if (rows.length) return rows[0].id;
+    // Someone else is inserting this very tag and hasn't committed yet.
+    await new Promise((r) => setTimeout(r, 20 * (attempt + 1)));
+  }
+  throw new Error(`Could not get an id for the tag “${name}”`);
 }
 
 // Sets a model's tags from an edit. A tag that stays keeps where it came from
@@ -314,9 +328,7 @@ async function setTags(client, modelId, tagNames) {
   const { rows: before } = await client.query('SELECT tag_id, source FROM model_tags WHERE model_id = $1', [modelId]);
   const sourceOf = new Map(before.map((r) => [r.tag_id, r.source]));
   await client.query('DELETE FROM model_tags WHERE model_id = $1', [modelId]);
-  for (const raw of tagNames) {
-    const name = String(raw).trim();
-    if (!name) continue;
+  for (const name of tagOrder(tagNames)) {
     const id = await tagId(client, name);
     await client.query(
       'INSERT INTO model_tags (model_id, tag_id, source) VALUES ($1,$2,$3) ON CONFLICT DO NOTHING',
@@ -329,7 +341,7 @@ async function setTags(client, modelId, tagNames) {
 async function replaceRuleTags(modelId, tagNames) {
   await db.transaction(async (client) => {
     const ids = [];
-    for (const name of tagNames) ids.push(await tagId(client, name));
+    for (const name of tagOrder(tagNames)) ids.push(await tagId(client, name));
     await client.query(
       `DELETE FROM model_tags WHERE model_id = $1 AND source = 'rule' AND NOT (tag_id = ANY($2::int[]))`, [modelId, ids]);
     for (const id of ids) {
@@ -350,8 +362,8 @@ async function removeTagsFrom(source) {
 // markTagged records that the model has had AI tags and a description.
 async function applyAiResult(modelId, { tags, description, overwriteDescription, name = null, markTagged = true }) {
   await db.transaction(async (client) => {
-    for (const name of tags) {
-      const id = await tagId(client, name);
+    for (const tagName of tagOrder(tags)) { // not `name`: that's this function's rename parameter
+      const id = await tagId(client, tagName);
       await client.query(`INSERT INTO model_tags (model_id, tag_id, source) VALUES ($1,$2,'ai') ON CONFLICT DO NOTHING`,
         [modelId, id]);
     }