diff --git a/app/sql.js b/app/sql.js
index 8c24d3e2a..48fcce7f6 100644
--- a/app/sql.js
+++ b/app/sql.js
@@ -458,6 +458,11 @@ async function updateToSchemaVersion6(currentVersion, instance) {
     );`
   );
 
+  await instance.run(`CREATE UNIQUE INDEX contact_prekey_identity_key_string_keyid ON contactPreKeys (
+    identityKeyString,
+    keyId
+  );`);
+
   await instance.run(
     `CREATE TABLE contactSignedPreKeys(
       id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
@@ -467,6 +472,11 @@ async function updateToSchemaVersion6(currentVersion, instance) {
     );`
   );
 
+  await instance.run(`CREATE UNIQUE INDEX contact_signed_prekey_identity_key_string_keyid ON contactSignedPreKeys (
+    identityKeyString,
+    keyId
+  );`);
+
   await instance.run('PRAGMA schema_version = 6;');
   await instance.run('COMMIT TRANSACTION;');
   console.log('updateToSchemaVersion6: success!');