diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index b2c57e87a5..30751fc8ac 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -3541,7 +3541,10 @@ estimate_hash_bucketsize(PlannerInfo *root, Node *hashkey, double nbuckets)
 	 * selectivity of rel's restriction clauses that mention the target Var.
 	 */
 	if (vardata.rel)
+	{
 		ndistinct *= vardata.rel->rows / vardata.rel->tuples;
+		ndistinct = clamp_row_est(ndistinct);
+	}
 
 	/*
 	 * Initial estimate of bucketsize fraction is 1/nbuckets as long as the