diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
index 9f4edbc60d8..f6f8d2eecc4 100644
--- a/src/backend/utils/adt/dbsize.c
+++ b/src/backend/utils/adt/dbsize.c
@@ -282,7 +282,18 @@ pg_tablespace_size_name(PG_FUNCTION_ARGS)
 static int64
 calculate_relation_size(RelFileNode *rfn, BackendId backend, ForkNumber forknum, char relpersistence)
 {
-	SMgrRelation  srel = smgropen(*rfn, backend, relpersistence);
+	SMgrRelation  srel;
+	RelFileNode zero = {0, 0, 0};
+
+	/*
+	 * We can get asked the size of a relation without storage, in which case
+	 * we get passed a zero RFL.
+	 * Return 0 for those relations.
+	 */
+	if (RelFileNodeEquals(*rfn, zero))
+		return 0;
+
+	srel = smgropen(*rfn, backend, relpersistence);
 
 	if (smgrexists(srel, forknum))
 	{