diff -r 00bfe5bd3553 Lib/sqlite3/test/transactions.py
--- a/Lib/sqlite3/test/transactions.py	Thu Nov 24 11:57:05 2016 -0800
+++ b/Lib/sqlite3/test/transactions.py	Fri Nov 25 11:35:41 2016 +0200
@@ -148,6 +148,15 @@
         with self.assertRaises(sqlite.InterfaceError):
             cur.fetchall()
 
+    def CheckManualTransaction(self):
+        """
+        This checks that we can start a transaction manually by calling
+        "begin immediate". See issue #28518.
+        """
+        self.cur1.execute("begin immediate")
+        with self.assertRaises(sqlite.OperationalError):
+            self.cur2.execute("create table test(x)")
+
 class SpecialCommandTests(unittest.TestCase):
     def setUp(self):
         self.con = sqlite.connect(":memory:")
diff -r 00bfe5bd3553 Modules/_sqlite/cursor.c
--- a/Modules/_sqlite/cursor.c	Thu Nov 24 11:57:05 2016 -0800
+++ b/Modules/_sqlite/cursor.c	Fri Nov 25 11:35:41 2016 +0200
@@ -564,6 +564,13 @@
                     goto error;
                 }
             } else {
+                /* patch for issue 28518 */
+                if (SQLITE_ERROR == rc &&
+                    strcmp("cannot start a transaction within a transaction",
+                           sqlite3_errmsg(self->connection->db)) == 0) {
+                    pysqlite_connection_rollback(self->connection, NULL);
+                    continue;
+                }
                 if (PyErr_Occurred()) {
                     /* there was an error that occurred in a user-defined callback */
                     if (_enable_callback_tracebacks) {