diff --git a/resources/sql/autopatches/20210215.changeset.02.phid-populate.php b/resources/sql/autopatches/20210215.changeset.02.phid-populate.php
--- a/resources/sql/autopatches/20210215.changeset.02.phid-populate.php
+++ b/resources/sql/autopatches/20210215.changeset.02.phid-populate.php
@@ -11,12 +11,20 @@
 
 $temporary_table = 'tmp_20210215_changeset_id_map';
 
-queryfx(
-  $conn,
-  'CREATE TEMPORARY TABLE %T (
-    changeset_id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
-    changeset_phid VARBINARY(64) NOT NULL)',
-  $temporary_table);
+try {
+  queryfx(
+    $conn,
+    'CREATE TEMPORARY TABLE %T (
+      changeset_id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+      changeset_phid VARBINARY(64) NOT NULL)',
+    $temporary_table);
+} catch (AphrontAccessDeniedQueryException $ex) {
+  throw new PhutilProxyException(
+    pht(
+      'Failed to "CREATE TEMPORARY TABLE". You may need to "GRANT" the '.
+      'current MySQL user this permission.'),
+    $ex);
+}
 
 $table_iterator = id(new LiskRawMigrationIterator($conn, $table_name))
   ->setPageSize($chunk_size);
diff --git a/src/infrastructure/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php b/src/infrastructure/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php
--- a/src/infrastructure/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php
+++ b/src/infrastructure/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php
@@ -347,7 +347,16 @@
       case 1142: // Access denied to table
       case 1143: // Access denied to column
       case 1227: // Access denied (e.g., no SUPER for SHOW SLAVE STATUS).
-        throw new AphrontAccessDeniedQueryException($message);
+
+        // See T13622. Try to help users figure out that this is a GRANT
+        // problem.
+
+        $more = pht(
+          'This error usually indicates that you need to "GRANT" the '.
+          'MySQL user additional permissions. See "GRANT" in the MySQL '.
+          'manual for help.');
+
+        throw new AphrontAccessDeniedQueryException("{$message}\n\n{$more}");
       case 1045: // Access denied (auth)
         throw new AphrontInvalidCredentialsQueryException($message);
       case 1146: // No such table