diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index 1593dbec21..12da689983 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -596,6 +596,7 @@ rel_supports_distinctness(PlannerInfo *root, RelOptInfo *rel)
                return false;
        if (rel->rtekind == RTE_RELATION)
        {
+               check_index_predicates(root, rel);
                /*
                 * For a plain relation, we only know how to prove uniqueness by
                 * reference to unique indexes.  Make sure there's at least one