diff --git a/ctr/src/lib.rs b/ctr/src/lib.rs
index 5b2d878..1199dbc 100644
--- a/ctr/src/lib.rs
+++ b/ctr/src/lib.rs
@@ -37,7 +37,7 @@
 //! }
 //! assert_eq!(buf[..], plaintext[..]);
 //!
-//! // CTR mode supports seeking
+//! // CTR mode supports seeking. The parameter is zero-based _bytes_ counter (not _blocks_).
 //! cipher.seek(0u32);
 //!
 //! // encrypt/decrypt from buffer to buffer