diff --git a/rcore-fs-sfs/src/lib.rs b/rcore-fs-sfs/src/lib.rs
index b3986d9..b5dd1c1 100644
--- a/rcore-fs-sfs/src/lib.rs
+++ b/rcore-fs-sfs/src/lib.rs
@@ -28,14 +28,14 @@ trait DeviceExt: Device {
         debug_assert!(offset + buf.len() <= BLKSIZE);
         match self.read_at(id * BLKSIZE + offset, buf) {
             Some(len) if len == buf.len() => Ok(()),
-            _ => panic!(),
+            _ => panic!("cannot read block {} offset {} from device", id, offset),
         }
     }
     fn write_block(&self, id: BlockId, offset: usize, buf: &[u8]) -> vfs::Result<()> {
         debug_assert!(offset + buf.len() <= BLKSIZE);
         match self.write_at(id * BLKSIZE + offset, buf) {
             Some(len) if len == buf.len() => Ok(()),
-            _ => panic!(),
+            _ => panic!("cannot write block {} offset {} to device", id, offset),
         }
     }
     /// Load struct `T` from given block in device
diff --git a/rust-toolchain b/rust-toolchain
new file mode 100644
index 0000000..bf867e0
--- /dev/null
+++ b/rust-toolchain
@@ -0,0 +1 @@
+nightly