diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 4283ce9f962..8bddd49cae4 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -3507,6 +3507,12 @@ estimate_path_cost_size(PlannerInfo *root,
 			{
 				Assert(foreignrel->reloptkind == RELOPT_UPPER_REL &&
 					   fpinfo->stage == UPPERREL_GROUP_AGG);
+				/*
+				 * Can only get here when this function is called from
+				 * add_foreign_ordered_paths() or add_foreign_final_paths();
+				 * in which cases, the passed-in fpextra should not be NULL.
+				 */
+				Assert(fpextra);
 				adjust_foreign_grouping_path_cost(root, pathkeys,
 												  retrieved_rows, width,
 												  fpextra->limit_tuples,