diff --git a/lib/store.js b/lib/store.js
index 5605e55..516f288 100644
--- a/lib/store.js
+++ b/lib/store.js
@@ -450,7 +450,9 @@ async function acceptCollectionSuggestion(name, modelIds = null) {
                           ORDER BY name = lower(name), name LIMIT 1), $1)
          RETURNING *`, [name]));
     }
-    const ids = waiting.map((w) => w.model_id);
+    // Sorted, so two of these at once take the model_projects rows in the same
+    // order rather than deadlocking on each other.
+    const ids = waiting.map((w) => w.model_id).sort((a, b) => a - b);
     for (const id of ids) {
       await client.query('INSERT INTO model_projects (model_id, project_id) VALUES ($1, $2) ON CONFLICT DO NOTHING', [id, project.id]);
     }
@@ -485,7 +487,7 @@ async function getAllTags() {
 // ---------------------------------------------------------------- projects
 async function setProjects(client, modelId, projectIds) {
   await client.query('DELETE FROM model_projects WHERE model_id = $1', [modelId]);
-  for (const pid of projectIds) {
+  for (const pid of [...projectIds].sort((a, b) => a - b)) { // one lock order, always
     await client.query(
       'INSERT INTO model_projects (model_id, project_id) VALUES ($1,$2) ON CONFLICT DO NOTHING',
       [modelId, pid]);