diff --git a/migrations/version_2_0_30.php b/migrations/version_2_0_30.php
index 1c75cb1..b3fa7fa 100644
--- a/migrations/version_2_0_30.php
+++ b/migrations/version_2_0_30.php
@@ -32,8 +32,15 @@ public function add_permission(): void
 		$this->db->sql_freeresult($result);
 		if (!$exists)
 		{
+			// An explicit id, like the options version_1_0_0 inserted: those
+			// left PostgreSQL's sequence at 1, so letting it pick one fails
+			// with a duplicate key on a fresh PostgreSQL board
+			$result = $this->db->sql_query('SELECT MAX(auth_option_id) AS max_id FROM ' . $this->table_prefix . 'kb_options');
+			$next_id = (int) $this->db->sql_fetchfield('max_id') + 1;
+			$this->db->sql_freeresult($result);
+
 			$this->db->sql_query('INSERT INTO ' . $this->table_prefix . 'kb_options ' . $this->db->sql_build_array('INSERT', [
-				'auth_option' => 'kb_m_change_author', 'is_global' => 0, 'is_local' => 1,
+				'auth_option_id' => $next_id, 'auth_option' => 'kb_m_change_author', 'is_global' => 0, 'is_local' => 1,
 			]));
 		}
 	}
diff --git a/migrations/version_2_0_31.php b/migrations/version_2_0_31.php
index 93d615f..8fea559 100644
--- a/migrations/version_2_0_31.php
+++ b/migrations/version_2_0_31.php
@@ -55,6 +55,28 @@ public function rebuild_match_index(): void
 			return;
 		}
 
+		// On PostgreSQL, version_1_0_3 created the index as plain un_mtch, but
+		// phpBB 3.3's tools find it by that name and then drop
+		// {table}_un_mtch, which does not exist. Drop whichever is there by
+		// its real name instead.
+		if ($this->db->get_sql_layer() === 'postgres' && !($this->db_tools instanceof \phpbb\db\tools\doctrine))
+		{
+			// Only this table's: another table may own an index called un_mtch
+			$result = $this->db->sql_query("SELECT indexname
+				FROM pg_indexes
+				WHERE tablename = '" . $this->db->sql_escape($table) . "'
+					AND " . $this->db->sql_in_set('indexname', ['un_mtch', $table . '_un_mtch']));
+			$indexes = array_column($this->db->sql_fetchrowset($result), 'indexname');
+			$this->db->sql_freeresult($result);
+
+			foreach ($indexes as $index)
+			{
+				$this->db->sql_query('DROP INDEX ' . $index);
+			}
+			$this->db_tools->sql_create_unique_index($table, 'un_mtch', self::MATCH_INDEX_COLUMNS);
+			return;
+		}
+
 		// phpBB 4.0 stores the index under the shortened table name, for example
 		// kbsrcwrdmtch_un_mtch, and only finds it by that full name
 		$stored_name = 'un_mtch';
diff --git a/tests/kb_options_id_migration_test.php b/tests/kb_options_id_migration_test.php
new file mode 100644
index 0000000..9fd67ad
--- /dev/null
+++ b/tests/kb_options_id_migration_test.php
@@ -0,0 +1,167 @@
+<?php
+/**
+ *
+ * Knowledge Base extension for the phpBB Forum Software package
+ *
+ * @copyright (c) 2026, phpBB Modders, https://www.phpbbmodders.com/
+ * @license GNU General Public License, version 2 (GPL-2.0)
+ *
+ */
+
+namespace phpbbmodders\knowledgebase\migrations;
+
+require_once __DIR__ . '/kb_extensions_test.php';
+require_once dirname(__DIR__) . '/migrations/version_1_0_0.php';
+require_once dirname(__DIR__) . '/migrations/version_1_0_3.php';
+require_once dirname(__DIR__) . '/migrations/version_2_0_2.php';
+require_once dirname(__DIR__) . '/migrations/version_2_0_15.php';
+require_once dirname(__DIR__) . '/migrations/version_2_0_30.php';
+require_once dirname(__DIR__) . '/migrations/version_2_0_31.php';
+if (!defined('CONFIG_TABLE')) define('CONFIG_TABLE', 'phpbb_config');
+
+/**
+ * Migrations that stopped a fresh PostgreSQL board from enabling the extension.
+ *
+ * version_2_0_30 adds kb_m_change_author after the seven options
+ * version_1_0_0 inserted with explicit ids. On PostgreSQL those inserts leave
+ * the table's sequence at 1, so the new option must not take its id from it.
+ *
+ * version_2_0_31 rebuilds the search-match index that version_1_0_3 created
+ * as plain un_mtch on PostgreSQL, where phpBB 3.3's tools drop it as
+ * {table}_un_mtch.
+ */
+class kb_options_id_migration_test extends \PHPUnit\Framework\TestCase
+{
+	private $db;
+	private $tools;
+	private $sqlite_fixture;
+
+	protected function tearDown(): void
+	{
+		if ($this->tools instanceof \phpbb\db\tools\doctrine) $this->tools->get_connection()->close();
+		if ($this->db) $this->db->sql_close();
+		if ($this->sqlite_fixture) @unlink($this->sqlite_fixture);
+	}
+
+	public function engines()
+	{
+		return [['sqlite'], ['mysql'], ['postgres']];
+	}
+
+	private function connect(string $engine): void
+	{
+		if ($engine === 'sqlite')
+		{
+			$this->db = new \phpbb\db\driver\sqlite3();
+			if (class_exists(\phpbb\db\tools\doctrine::class))
+			{
+				$this->sqlite_fixture = tempnam(sys_get_temp_dir(), 'kb-options-');
+				$this->assertTrue($this->db->sql_connect($this->sqlite_fixture, '', '', ''));
+				$this->tools = new \phpbb\db\tools\doctrine(\phpbb\db\doctrine\connection_factory::get_connection_from_params('sqlite3', $this->sqlite_fixture));
+				$this->tools->set_table_prefix('phpbb_');
+			}
+			else
+			{
+				$this->assertTrue($this->db->sql_connect(':memory:', '', '', ''));
+				$this->tools = new \phpbb\db\tools\sqlite3($this->db);
+			}
+			return;
+		}
+
+		$port = getenv('KB_TEST_' . strtoupper($engine) . '_PORT');
+		if (!$port) $this->markTestSkipped('Set the fixture database port to run integration tests');
+		$this->assertTrue(ctype_digit($port));
+		$this->db = $engine === 'mysql' ? new \phpbb\db\driver\mysqli() : new \phpbb\db\driver\postgres();
+		$this->assertIsObject($this->db->sql_connect('127.0.0.1', $engine === 'mysql' ? 'root' : 'postgres', '', 'kb_fixture', (int) $port));
+		if (class_exists(\phpbb\db\tools\doctrine::class))
+		{
+			$this->tools = new \phpbb\db\tools\doctrine(\phpbb\db\doctrine\connection_factory::get_connection_from_params(
+				$engine === 'mysql' ? 'mysqli' : 'postgres', '127.0.0.1', $engine === 'mysql' ? 'root' : 'postgres', '', 'kb_fixture', $port
+			));
+			$this->tools->set_table_prefix('phpbb_');
+		}
+		else
+		{
+			$this->tools = $engine === 'mysql' ? new \phpbb\db\tools\tools($this->db) : new \phpbb\db\tools\postgres($this->db);
+		}
+	}
+
+	/** @dataProvider engines */
+	public function test_the_author_permission_is_added_after_the_first_options_on_a_fresh_board($engine)
+	{
+		$this->connect($engine);
+		foreach (['phpbb_kb_options', 'phpbb_kb_users', 'phpbb_kb_groups'] as $table)
+		{
+			if ($this->tools->sql_table_exists($table)) $this->tools->sql_table_drop($table);
+			if ($this->db->get_sql_layer() === 'postgres') $this->db->sql_query('DROP SEQUENCE IF EXISTS ' . $table . '_seq');
+		}
+
+		// The options table and its first seven options, exactly as version_1_0_0 makes them
+		$config = new \phpbb\config\config([]);
+		$first = new version_1_0_0($config, $this->db, $this->tools, '', 'php', 'phpbb_', []);
+		$this->tools->sql_create_table('phpbb_kb_options', $first->update_schema()['add_tables']['phpbb_kb_options']);
+		$first->update_kb_options_table();
+
+		(new version_2_0_30($config, $this->db, $this->tools, '', 'php', 'phpbb_', []))->add_permission();
+
+		$result = $this->db->sql_query('SELECT auth_option_id, auth_option FROM phpbb_kb_options ORDER BY auth_option_id');
+		$options = [];
+		while ($row = $this->db->sql_fetchrow($result))
+		{
+			$options[(int) $row['auth_option_id']] = $row['auth_option'];
+		}
+		$this->db->sql_freeresult($result);
+
+		$this->assertSame('kb_m_change_author', $options[8] ?? null);
+		$this->assertCount(8, $options);
+
+		// Running it again adds nothing
+		(new version_2_0_30($config, $this->db, $this->tools, '', 'php', 'phpbb_', []))->add_permission();
+		$result = $this->db->sql_query('SELECT COUNT(*) AS total FROM phpbb_kb_options');
+		$this->assertSame(8, (int) $this->db->sql_fetchfield('total'));
+		$this->db->sql_freeresult($result);
+
+		$this->tools->sql_table_drop('phpbb_kb_options');
+		if ($this->db->get_sql_layer() === 'postgres') $this->db->sql_query('DROP SEQUENCE IF EXISTS phpbb_kb_options_seq');
+	}
+
+	/** @dataProvider engines */
+	public function test_the_search_match_index_is_rebuilt_after_version_1_0_3_made_it($engine)
+	{
+		$this->connect($engine);
+		$table = 'phpbb_kb_src_wrdmtch';
+		foreach ([$table, 'phpbb_kb_articles'] as $name)
+		{
+			if ($this->tools->sql_table_exists($name)) $this->tools->sql_table_drop($name);
+		}
+		// version_1_0_3 also drops a kb_articles column
+		$this->tools->sql_create_table('phpbb_kb_articles', ['COLUMNS' => ['article_id' => ['UINT', 0], 'bbcode_bitfield' => ['VCHAR:32', '']]]);
+
+		// The table as version_1_0_0, 1_0_3 (schema and data), 2_0_2 and 2_0_15 leave it
+		$config = new \phpbb\config\config([]);
+		$migration = fn($class) => new $class($config, $this->db, $this->tools, '', 'php', 'phpbb_', []);
+		$this->tools->sql_create_table($table, $migration(version_1_0_0::class)->update_schema()['add_tables'][$table]);
+		$this->tools->perform_schema_changes($migration(version_1_0_3::class)->update_schema());
+		$migration(version_1_0_3::class)->add_key();
+		$this->tools->perform_schema_changes($migration(version_2_0_2::class)->update_schema());
+		$this->tools->perform_schema_changes($migration(version_2_0_15::class)->update_schema());
+		$this->db->sql_query('INSERT INTO ' . $table . ' (article_id, word_id, title_match, descr_match) VALUES (1, 1, 0, 1)');
+
+		$migration(version_2_0_31::class)->rebuild_match_index();
+		// Run again (an enable retried): still fine
+		$migration(version_2_0_31::class)->rebuild_match_index();
+
+		// The match survives, and the four-column unique key holds
+		$result = $this->db->sql_query('SELECT COUNT(*) AS total FROM ' . $table);
+		$this->assertSame(1, (int) $this->db->sql_fetchfield('total'));
+		$this->db->sql_freeresult($result);
+		$this->db->sql_return_on_error(true);
+		$duplicate = $this->db->sql_query('INSERT INTO ' . $table . ' (article_id, word_id, title_match, descr_match) VALUES (1, 1, 0, 1)');
+		$this->db->sql_return_on_error(false);
+		$this->assertFalse($duplicate, 'a duplicate match should be refused by the unique index');
+		$this->assertNotFalse($this->db->sql_query('INSERT INTO ' . $table . ' (article_id, word_id, title_match, descr_match) VALUES (1, 1, 0, 0)'));
+
+		$this->tools->sql_table_drop($table);
+		$this->tools->sql_table_drop('phpbb_kb_articles');
+	}
+}