diff --git a/lfs.c b/lfs.c
index 624f43cc..967e7c42 100644
--- a/lfs.c
+++ b/lfs.c
@@ -93,6 +93,7 @@ static int lfs_bd_read(lfs_t *lfs,
             // bypass cache?
             diff = lfs_aligndown(diff, lfs->cfg->read_size);
             int err = lfs->cfg->read(lfs->cfg, block, off, data, diff);
+            LFS_ASSERT(err <= 0);
             if (err) {
                 return err;
             }
@@ -739,6 +740,7 @@ static lfs_stag_t lfs_dir_getslice(lfs_t *lfs, const lfs_mdir_t *dir,
         int err = lfs_bd_read(lfs,
                 NULL, &lfs->rcache, sizeof(ntag),
                 dir->pair[0], off, &ntag, sizeof(ntag));
+        LFS_ASSERT(err <= 0);
         if (err) {
             return err;
         }
@@ -767,6 +769,7 @@ static lfs_stag_t lfs_dir_getslice(lfs_t *lfs, const lfs_mdir_t *dir,
             err = lfs_bd_read(lfs,
                     NULL, &lfs->rcache, diff,
                     dir->pair[0], off+sizeof(tag)+goff, gbuffer, diff);
+            LFS_ASSERT(err <= 0);
             if (err) {
                 return err;
             }