diff --git a/zipl/src/zipl_helper.device-mapper.c b/zipl/src/zipl_helper.device-mapper.c
index 3a44735f..91308cef 100644
--- a/zipl/src/zipl_helper.device-mapper.c
+++ b/zipl/src/zipl_helper.device-mapper.c
@@ -860,7 +860,7 @@ static int get_physical_device(struct physical_device *pd, dev_t dev,
 				   target_entry_new(makedev(major, minor), target));
 		table_free(table);
 		/* Convert fs_start to offset on parent target */
-		start -= target->start;
+		start += target->start;
 	}
 }