diff --git a/docs/release.rst b/docs/release.rst
index c5a14f1d..2aa528f6 100644
--- a/docs/release.rst
+++ b/docs/release.rst
@@ -14,6 +14,25 @@ Release notes
 
 .. _unreleased:
 
+Unreleased
+----------
+
+Enhancements
+~~~~~~~~~~~~
+
+Improvements
+~~~~~~~~~~~~
+
+Fixes
+~~~~~
+
+* Fix ``const`` discard warnings in ``fletcher32``.
+  By :user:`John Kirkham <jakirkham>`, :issue:`728`
+
+Maintenance
+~~~~~~~~~~~
+
+
 0.16.0
 ------
 
diff --git a/numcodecs/fletcher32.pyx b/numcodecs/fletcher32.pyx
index 387295b6..56a5f793 100644
--- a/numcodecs/fletcher32.pyx
+++ b/numcodecs/fletcher32.pyx
@@ -76,7 +76,7 @@ class Fletcher32(Codec):
         """Return buffer plus a footer with the fletcher checksum (4-bytes)"""
         buf = ensure_contiguous_ndarray(buf).ravel().view('uint8')
         cdef const uint8_t[::1] b_mv = buf
-        cdef uint8_t* b_ptr = &b_mv[0]
+        cdef const uint8_t* b_ptr = &b_mv[0]
         cdef Py_ssize_t b_len = len(b_mv)
 
         cdef Py_ssize_t out_len = b_len + FOOTER_LENGTH
@@ -92,7 +92,7 @@ class Fletcher32(Codec):
         """Check fletcher checksum, and return buffer without it"""
         b = ensure_contiguous_ndarray(buf).view('uint8')
         cdef const uint8_t[::1] b_mv = b
-        cdef uint8_t* b_ptr = &b_mv[0]
+        cdef const uint8_t* b_ptr = &b_mv[0]
         cdef Py_ssize_t b_len = len(b_mv)
 
         val = _fletcher32(b_mv[:-FOOTER_LENGTH])