diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 99284cb6de1..d8aa35dee79 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -2964,7 +2964,8 @@ choose_hashed_distinct(PlannerInfo *root,
  * 'groupColIdx' receives an array of column numbers for the GROUP BY
  *			expressions (if there are any) in the returned target list.
  * 'need_tlist_eval' is set true if we really need to evaluate the
- *			returned tlist as-is.
+ *			returned tlist as-is.  (Note: locate_grouping_columns assumes
+ *			that if this is FALSE, all grouping columns are simple Vars.)
  *
  * The result is the targetlist to be passed to query_planner.
  */
@@ -3127,6 +3128,7 @@ get_grouping_column_index(Query *parse, TargetEntry *tle)
  * This is only needed if we don't use the sub_tlist chosen by
  * make_subplanTargetList.	We have to forget the column indexes found
  * by that routine and re-locate the grouping exprs in the real sub_tlist.
+ * We assume the grouping exprs are just Vars (see make_subplanTargetList).
  */
 static void
 locate_grouping_columns(PlannerInfo *root,
@@ -3150,11 +3152,24 @@ locate_grouping_columns(PlannerInfo *root,
 	foreach(gl, root->parse->groupClause)
 	{
 		SortGroupClause *grpcl = (SortGroupClause *) lfirst(gl);
-		Node	   *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
-		TargetEntry *te = tlist_member(groupexpr, sub_tlist);
+		Var		   *groupexpr = (Var *) get_sortgroupclause_expr(grpcl, tlist);
+		TargetEntry *te;
 
+		/*
+		 * The grouping column returned by create_plan might not have the same
+		 * typmod as the original Var.	(This can happen in cases where a
+		 * set-returning function has been inlined, so that we now have more
+		 * knowledge about what it returns than we did when the original Var
+		 * was created.)  So we can't use tlist_member() to search the tlist;
+		 * instead use tlist_member_match_var.	For safety, still check that
+		 * the vartype matches.
+		 */
+		if (!(groupexpr && IsA(groupexpr, Var)))
+			elog(ERROR, "grouping column is not a Var as expected");
+		te = tlist_member_match_var(groupexpr, sub_tlist);
 		if (!te)
 			elog(ERROR, "failed to locate grouping columns");
+		Assert(((Var *) te->expr)->vartype == groupexpr->vartype);
 		groupColIdx[keyno++] = te->resno;
 	}
 }
diff --git a/src/backend/optimizer/util/tlist.c b/src/backend/optimizer/util/tlist.c
index 5dc4b835fa3..5cc3cdc15a6 100644
--- a/src/backend/optimizer/util/tlist.c
+++ b/src/backend/optimizer/util/tlist.c
@@ -71,6 +71,35 @@ tlist_member_ignore_relabel(Node *node, List *targetlist)
 	return NULL;
 }
 
+/*
+ * tlist_member_match_var
+ *	  Same as above, except that we match the provided Var on the basis
+ *	  of varno/varattno/varlevelsup only, rather than using full equal().
+ *
+ * This is needed in some cases where we can't be sure of an exact typmod
+ * match.  It's probably a good idea to check the vartype anyway, but
+ * we leave it to the caller to apply any suitable sanity checks.
+ */
+TargetEntry *
+tlist_member_match_var(Var *var, List *targetlist)
+{
+	ListCell   *temp;
+
+	foreach(temp, targetlist)
+	{
+		TargetEntry *tlentry = (TargetEntry *) lfirst(temp);
+		Var		   *tlvar = (Var *) tlentry->expr;
+
+		if (!tlvar || !IsA(tlvar, Var))
+			continue;
+		if (var->varno == tlvar->varno &&
+			var->varattno == tlvar->varattno &&
+			var->varlevelsup == tlvar->varlevelsup)
+			return tlentry;
+	}
+	return NULL;
+}
+
 /*
  * flatten_tlist
  *	  Create a target list that only contains unique variables.
diff --git a/src/include/optimizer/tlist.h b/src/include/optimizer/tlist.h
index 0d6f05199ae..ad01f2e4856 100644
--- a/src/include/optimizer/tlist.h
+++ b/src/include/optimizer/tlist.h
@@ -19,6 +19,7 @@
 
 extern TargetEntry *tlist_member(Node *node, List *targetlist);
 extern TargetEntry *tlist_member_ignore_relabel(Node *node, List *targetlist);
+extern TargetEntry *tlist_member_match_var(Var *var, List *targetlist);
 
 extern List *flatten_tlist(List *tlist, PVCAggregateBehavior aggbehavior,
 			  PVCPlaceHolderBehavior phbehavior);
diff --git a/src/test/regress/expected/rangefuncs.out b/src/test/regress/expected/rangefuncs.out
index 45ffd85b1b7..37391dcfce7 100644
--- a/src/test/regress/expected/rangefuncs.out
+++ b/src/test/regress/expected/rangefuncs.out
@@ -1247,6 +1247,17 @@ SELECT * FROM foo(3);
 (9 rows)
 
 DROP FUNCTION foo(int);
+-- case that causes change of typmod knowledge during inlining
+CREATE OR REPLACE FUNCTION foo()
+RETURNS TABLE(a varchar(5))
+AS $$ SELECT 'hello'::varchar(5) $$ LANGUAGE sql STABLE;
+SELECT * FROM foo() GROUP BY 1;
+   a   
+-------
+ hello
+(1 row)
+
+DROP FUNCTION foo();
 --
 -- some tests on SQL functions with RETURNING
 --
diff --git a/src/test/regress/sql/rangefuncs.sql b/src/test/regress/sql/rangefuncs.sql
index d522cdb10e4..e82a1d55712 100644
--- a/src/test/regress/sql/rangefuncs.sql
+++ b/src/test/regress/sql/rangefuncs.sql
@@ -330,6 +330,13 @@ AS $$ SELECT a, b
 SELECT * FROM foo(3);
 DROP FUNCTION foo(int);
 
+-- case that causes change of typmod knowledge during inlining
+CREATE OR REPLACE FUNCTION foo()
+RETURNS TABLE(a varchar(5))
+AS $$ SELECT 'hello'::varchar(5) $$ LANGUAGE sql STABLE;
+SELECT * FROM foo() GROUP BY 1;
+DROP FUNCTION foo();
+
 --
 -- some tests on SQL functions with RETURNING
 --