diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 6c873ca091..e194827c93 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -1,13 +1,13 @@
 Change Log
 ==========
 
-0.13.1: 2020/07/21
+0.13.1: 2020/07/22
 ------------------
 
 Bug fix release:
 
 * `silx.gui.plot.dialog`: Fixed `ColormapDialog` custom range input (PR #3155)
-
+* Build: Fixed cython 3 compatibility (PR #3163).
 * Documentation: Update version number and changelog (PR #3156)
 
 
diff --git a/silx/math/colormap.pyx b/silx/math/colormap.pyx
index dde249dfb6..2495f3c5aa 100644
--- a/silx/math/colormap.pyx
+++ b/silx/math/colormap.pyx
@@ -453,6 +453,8 @@ def _cmap(data_types[:] data,
     :param nan_color: Color to use for NaN value.
     :return: The generated image
     """
+    cdef image_types[:, ::1] output
+
     # Proxy for calling the right implementation depending on data type
     if data_types in lut_types:  # Use LUT implementation
         output = compute_cmap_with_lut(