Index: test/window1.test
==================================================================
--- test/window1.test
+++ test/window1.test
@@ -594,17 +594,31 @@
 } {
 }
 
 # 2018-12-06
 # https://www.sqlite.org/src/info/f09fcd17810f65f7
-# Assertion fault when window functions are used
+# Assertion fault when window functions are used.
+#
+# Root cause is the query flattener invoking sqlite3ExprDup() on
+# expressions that contain subqueries with window functions.  The
+# sqlite3ExprDup() routine is not making correctly initializing
+# Select.pWin field of the subqueries.
 #
 sqlite3 db :memory:
 do_execsql_test 14.0 {
   SELECT * FROM(
     SELECT * FROM (SELECT 1 AS c) WHERE c IN (
         SELECT (row_number() OVER()) FROM (VALUES (0))
     )
   );
 } {1}
+do_execsql_test 14.1 {
+  CREATE TABLE t1(x); INSERT INTO t1(x) VALUES(12345);
+  CREATE TABLE t2(c); INSERT INTO t2(c) VALUES(1);
+  SELECT y, y+1, y+2 FROM (
+    SELECT c IN (
+      SELECT (row_number() OVER()) FROM t1
+    ) AS y FROM t2
+  );
+} {1 2 3}
 
 finish_test