diff --git a/fs_mgr/fs_mgr_slotselect.cpp b/fs_mgr/fs_mgr_slotselect.cpp
index f3bba7b93..f27a79db1 100644
--- a/fs_mgr/fs_mgr_slotselect.cpp
+++ b/fs_mgr/fs_mgr_slotselect.cpp
@@ -37,8 +37,7 @@ int fs_mgr_update_for_slotselect(struct fstab *fstab)
                 got_suffix = 1;
             }
 
-            if (asprintf(&tmp, "%s%s", fstab->recs[n].blk_device,
-                         suffix.c_str()) > 0) {
+            if (asprintf(&tmp, "%s_%s", fstab->recs[n].blk_device, suffix.c_str()) > 0) {
                 free(fstab->recs[n].blk_device);
                 fstab->recs[n].blk_device = tmp;
             } else {