diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index dcaea7135f..64385d56d1 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -1285,6 +1285,8 @@ heapam_index_build_range_scan(Relation heapRelation,
 	}
 
 	reltuples = 0;
+	MemSet(root_offsets, InvalidOffsetNumber,
+		   MaxHeapTuplesPerPage);
 
 	/*
 	 * Scan all tuples in the base relation.