diff --git a/src/backend/postmaster/checksumhelper.c b/src/backend/postmaster/checksumhelper.c
index 9186dbea22..62d5b7b9c8 100644
--- a/src/backend/postmaster/checksumhelper.c
+++ b/src/backend/postmaster/checksumhelper.c
@@ -88,6 +88,25 @@ StartChecksumHelperLauncher(int cost_delay, int cost_limit)
 {
 	BackgroundWorker bgw;
 	BackgroundWorkerHandle *bgw_handle;
+	HeapTuple	tup;
+	Relation	rel;
+	HeapScanDesc scan;
+
+	/*
+	 * Check that all databases allow connections, while we can still send
+	 * an error message to the client.
+	 */
+	rel = heap_open(DatabaseRelationId, AccessShareLock);
+	scan = heap_beginscan_catalog(rel, 0, NULL);
+
+	while (HeapTupleIsValid(tup = heap_getnext(scan, ForwardScanDirection)))
+	{
+		Form_pg_database pgdb = (Form_pg_database) GETSTRUCT(tup);
+		if (!pgdb->datallowconn)
+			ereport(ERROR,
+					(errmsg("database \"%s\" does not allow connections.", NameStr(pgdb->datname)),
+					 errhint("Allow connections using ALTER DATABASE and try again.")));
+	}
 
 	if (!pg_atomic_test_set_flag(&ChecksumHelperShmem->launcher_started))
 	{