Index: src/select.c
==================================================================
--- src/select.c
+++ src/select.c
@@ -3299,11 +3299,12 @@
 **        and (2b) the outer query does not use subqueries other than the one
 **        FROM-clause subquery that is a candidate for flattening.  (2b is
 **        due to ticket [2f7170d73bf9abf80] from 2015-02-09.)
 **
 **   (3)  The subquery is not the right operand of a LEFT JOIN
-**        or the subquery is not itself a join.
+**        or the subquery is not itself a join and the outer query is not
+**        an aggregate.
 **
 **   (4)  The subquery is not DISTINCT.
 **
 **  (**)  At one point restrictions (4) and (5) defined a subset of DISTINCT
 **        sub-queries that were excluded from this optimization. Restriction 
@@ -3494,16 +3495,21 @@
   ** If we flatten the above, we would get
   **
   **         (t1 LEFT OUTER JOIN t2) JOIN t3
   **
   ** which is not at all the same thing.
+  **
+  ** If the subquery is the right operand of a LEFT JOIN, then the outer
+  ** query cannot be an aggregate.  This is an artifact of the way aggregates
+  ** are processed - there is not mechanism to determine if the LEFT JOIN
+  ** table should be all-NULL.
   **
   ** See also tickets #306, #350, and #3300.
   */
   if( (pSubitem->fg.jointype & JT_OUTER)!=0 ){
     isLeftJoin = 1;
-    if( pSubSrc->nSrc>1 ){
+    if( pSubSrc->nSrc>1 || isAgg ){
       return 0; /* Restriction (3) */
     }
   }
 
   /* Restriction 17: If the sub-query is a compound SELECT, then it must

Index: test/join.test
==================================================================
--- test/join.test
+++ test/join.test
@@ -729,7 +729,18 @@
 do_execsql_test join-14.3 {
   SELECT *
   FROM (SELECT 111)
   LEFT JOIN (SELECT cc+222, * FROM (SELECT * FROM (SELECT 333 cc)));
 } {111 555 333}
+
+do_execsql_test join-14.4 {
+  DROP TABLE IF EXISTS t1;
+  CREATE TABLE t1(c PRIMARY KEY, a TEXT(10000), b TEXT(10000));
+  SELECT * FROM (SELECT 111) LEFT JOIN (SELECT c+222 FROM t1) GROUP BY 1;
+} {111 {}}
+do_execsql_test join-14.5 {
+  DROP TABLE IF EXISTS t1;
+  CREATE TABLE t1(c PRIMARY KEY) WITHOUT ROWID;
+  SELECT * FROM (SELECT 111) LEFT JOIN (SELECT c+222 FROM t1) GROUP BY 1;
+} {111 {}}
 
 finish_test