diff --git a/CHANGELOG.md b/CHANGELOG.md
index d17a2ec..7ee59ab 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- **Postgres open-transaction probe (#787)** — `BEGIN` + `SELECT` does not assign an XID, so `pg_current_xact_id_if_assigned` stayed NULL (SQL-tab badge off; autocommit-off prepended a second `BEGIN`). The session tracks BEGIN/COMMIT/ROLLBACK and otherwise probes `pg_stat_activity.xact_start` (PG 9+). Implicit BEGIN when autocommit is off stays a separate `execute`.
 - **Postgres Table Browser paging (#788)** — Browse stays on `PgSessionMode.readOnly`. `SELECT` uses `ORDER BY` primary-key columns when a PK exists. Row totals come from `pg_class.reltuples` instead of a blocking `COUNT(*)` before first paint (stale estimates below the current page are ignored so Next still works). Save / REFRESH stay on `tableWrite`.
 - **Postgres timestamptz / bytea / jsonb / arrays (#789)** — Table Browser and SQL results encode cells as PG literals (ISO timestamps, `\x` hex for bytea, JSON text for jsonb, `{1,2,3}` for arrays) instead of `Object.toString`. Schema uses `udt_name` so `ARRAY` / `USER-DEFINED` round-trip through `formatLiteral`.
 - **Postgres host/port SSL (#790)** — Host/port Use SSL/TLS stays `sslmode=require` (encrypt, no CA check) unless a Root CA is set, then `verify-full`. A URI `sslmode=` value still wins. The form documents the MITM tradeoff and writes `sslmode=verify-full` when saving a Root CA.
diff --git a/lib/core/database/postgres_connection.dart b/lib/core/database/postgres_connection.dart
index 0967096..8507de0 100644
--- a/lib/core/database/postgres_connection.dart
+++ b/lib/core/database/postgres_connection.dart
@@ -11,6 +11,7 @@ import 'package:postgres/src/connection_string.dart' show parseConnectionString;
 
 import 'postgres_metadata.dart';
 import 'postgres_result_cells.dart';
+import 'postgres_sql.dart';
 import 'table_schema_meta.dart';
 
 /// Replaces the database in a `postgresql://` / `postgres://` URI (path or
@@ -131,6 +132,7 @@ class PostgresConnection {
 
   Connection? _conn;
   bool _isConnected = false;
+  bool _inTransaction = false;
 
   bool get isConnected => _isConnected && _conn != null;
 
@@ -238,6 +240,7 @@ class PostgresConnection {
         );
       }
       _isConnected = true;
+      _inTransaction = false;
       scrubCredentials();
     } catch (e, st) {
       _isConnected = false;
@@ -255,6 +258,7 @@ class PostgresConnection {
 
   Future<void> disconnect() async {
     _isConnected = false;
+    _inTransaction = false;
     final c = _conn;
     _conn = null;
     try {
@@ -268,6 +272,7 @@ class PostgresConnection {
   /// cancelling a long query or [PostgresService.interrupt].
   Future<void> forceClose() async {
     _isConnected = false;
+    _inTransaction = false;
     final c = _conn;
     _conn = null;
     try {
@@ -313,7 +318,9 @@ class PostgresConnection {
       throw StateError('Not connected to PostgreSQL');
     }
     try {
-      return await _conn!.execute(sql, timeout: timeout);
+      final result = await _conn!.execute(sql, timeout: timeout);
+      _inTransaction = applyPostgresTransactionSql(_inTransaction, sql);
+      return result;
     } on TimeoutException {
       unawaited(forceClose());
       rethrow;
@@ -335,19 +342,24 @@ class PostgresConnection {
     }
   }
 
-  /// Whether the session has an open transaction (PostgreSQL 13+).
-  /// Returns `null` if the server does not support the probe or an error occurs.
+  /// Whether the session has an open transaction.
+  ///
+  /// `BEGIN` + `SELECT` does not assign an XID, so `pg_current_xact_id_if_assigned`
+  /// stays NULL. We track BEGIN/COMMIT/ROLLBACK on [execute], and otherwise
+  /// probe `pg_stat_activity.xact_start` for this backend (PG 9+; no PG 13
+  /// requirement). Returns `null` only when disconnected.
   Future<bool?> inOpenTransaction() async {
     if (!isConnected || _conn == null) return null;
+    if (_inTransaction) return true;
     try {
-      final r = await _conn!.execute(
-        'SELECT pg_current_xact_id_if_assigned() IS NOT NULL',
-      );
-      if (r.isEmpty) return null;
-      return r.first[0] as bool;
+      final r = await _conn!.execute(kPostgresOpenTransactionProbeSql);
+      if (r.isEmpty) return false;
+      final open = r.first[0] == true;
+      _inTransaction = open;
+      return open;
     } catch (e) {
       debugPrint('PostgresConnection.inOpenTransaction: $e');
-      return null;
+      return _inTransaction;
     }
   }
 
diff --git a/lib/core/database/postgres_sql.dart b/lib/core/database/postgres_sql.dart
index d565506..fd746b0 100644
--- a/lib/core/database/postgres_sql.dart
+++ b/lib/core/database/postgres_sql.dart
@@ -27,6 +27,47 @@ bool shouldSkipImplicitBegin(String sql) {
   return false;
 }
 
+/// Own-backend `xact_start` (set at `BEGIN`, even when no XID is assigned).
+///
+/// Replaces `pg_current_xact_id_if_assigned()` (PG 13+), which stays NULL after
+/// `BEGIN` + `SELECT`. `pg_stat_activity.xact_start` exists on PG 9+.
+const kPostgresOpenTransactionProbeSql =
+    'SELECT xact_start IS NOT NULL '
+    'FROM pg_catalog.pg_stat_activity '
+    'WHERE pid = pg_backend_pid()';
+
+/// Updates session tx state from a successfully executed statement.
+///
+/// `BEGIN` / `START TRANSACTION` open; `COMMIT` / `END` / `ROLLBACK` close.
+/// `ROLLBACK TO` (savepoint) leaves the transaction open.
+bool applyPostgresTransactionSql(bool currentlyOpen, String sql) {
+  final s = stripLeadingWhitespaceAndLineComments(sql);
+  if (s.isEmpty) return currentlyOpen;
+  final u = s.toUpperCase();
+
+  if (u.startsWith('START TRANSACTION') || _pgTxStartsWithKeyword(u, 'BEGIN')) {
+    return true;
+  }
+  if (_pgTxStartsWithKeyword(u, 'COMMIT') || _pgTxStartsWithKeyword(u, 'END')) {
+    return false;
+  }
+  if (_pgTxStartsWithKeyword(u, 'ROLLBACK')) {
+    if (RegExp(r'^ROLLBACK\s+TO\b').hasMatch(u)) return currentlyOpen;
+    return false;
+  }
+  return currentlyOpen;
+}
+
+bool _pgTxStartsWithKeyword(String upper, String kw) {
+  if (!upper.startsWith(kw)) return false;
+  if (upper.length == kw.length) return true;
+  final next = upper.codeUnitAt(kw.length);
+  final isIdent = (next >= 0x41 && next <= 0x5a) ||
+      next == 0x5f ||
+      (next >= 0x30 && next <= 0x39);
+  return !isIdent;
+}
+
 /// Runs [statements] as separate extended-protocol executes inside BEGIN/COMMIT.
 ///
 /// PostgreSQL Parse cannot contain multiple commands, so
diff --git a/lib/features/postgresql/postgres_sql_workspace.dart b/lib/features/postgresql/postgres_sql_workspace.dart
index 8574f96..b6a06fd 100644
--- a/lib/features/postgresql/postgres_sql_workspace.dart
+++ b/lib/features/postgresql/postgres_sql_workspace.dart
@@ -450,6 +450,7 @@ class _PostgresSqlWorkspaceState extends material.State<PostgresSqlWorkspace> {
       if (!_autocommit) {
         final inTx = await conn.inOpenTransaction() ?? false;
         if (!inTx && !shouldSkipImplicitBegin(sql)) {
+          // Separate execute: Parse cannot take `BEGIN;` + the next statement.
           await conn.execute('BEGIN', timeout: to);
         }
       }
diff --git a/test/core/database/postgres_sql_test.dart b/test/core/database/postgres_sql_test.dart
index fd69b46..efec076 100644
--- a/test/core/database/postgres_sql_test.dart
+++ b/test/core/database/postgres_sql_test.dart
@@ -80,6 +80,60 @@ void main() {
     });
   });
 
+  group('applyPostgresTransactionSql', () {
+    test('BEGIN + SELECT stays open; COMMIT closes', () {
+      var open = false;
+      open = applyPostgresTransactionSql(open, 'BEGIN');
+      expect(open, isTrue);
+      open = applyPostgresTransactionSql(open, 'SELECT 1');
+      expect(open, isTrue);
+      open = applyPostgresTransactionSql(open, 'COMMIT');
+      expect(open, isFalse);
+    });
+
+    test('BEGIN WORK opens; BEGINNING does not', () {
+      expect(applyPostgresTransactionSql(false, 'BEGIN WORK'), isTrue);
+      expect(applyPostgresTransactionSql(false, 'BEGINNING'), isFalse);
+    });
+
+    test('START TRANSACTION and END', () {
+      var open = applyPostgresTransactionSql(false, 'START TRANSACTION');
+      expect(open, isTrue);
+      open = applyPostgresTransactionSql(open, 'END');
+      expect(open, isFalse);
+    });
+
+    test('ROLLBACK closes; ROLLBACK TO savepoint does not', () {
+      expect(applyPostgresTransactionSql(true, 'ROLLBACK'), isFalse);
+      expect(
+        applyPostgresTransactionSql(true, 'ROLLBACK TO sp1'),
+        isTrue,
+      );
+      expect(
+        applyPostgresTransactionSql(true, 'ROLLBACK TO SAVEPOINT sp1'),
+        isTrue,
+      );
+    });
+
+    test('strips leading comments before BEGIN', () {
+      expect(
+        applyPostgresTransactionSql(false, '-- note\nBEGIN'),
+        isTrue,
+      );
+    });
+  });
+
+  group('kPostgresOpenTransactionProbeSql', () {
+    test('uses xact_start, not xid-if-assigned', () {
+      expect(kPostgresOpenTransactionProbeSql, contains('xact_start'));
+      expect(kPostgresOpenTransactionProbeSql, contains('pg_backend_pid()'));
+      expect(
+        kPostgresOpenTransactionProbeSql,
+        isNot(contains('pg_current_xact_id')),
+      );
+    });
+  });
+
   group('runPostgresStatementsInTransaction', () {
     test('executes BEGIN, each statement, COMMIT as separate calls', () async {
       final calls = <String>[];