diff --git a/CHANGES.md b/CHANGES.md
index 89702f9..b1bad66 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,9 @@
 # Release Notes
 
+## 5.1.1 (2024-01-08)
+
+* use morecantile `TileMatrixSet.cellSize` property instead of deprecated/private `TileMatrixSet._resolution` method
+
 ## 5.1.0 (2023-12-11)
 
 * add option to write progress to an external text buffer (author @SellersEvan, https://github.com/cogeotiff/rio-cogeo/pull/273)
diff --git a/rio_cogeo/utils.py b/rio_cogeo/utils.py
index 36d133d..ffd198b 100644
--- a/rio_cogeo/utils.py
+++ b/rio_cogeo/utils.py
@@ -126,7 +126,7 @@ def get_web_optimized_params(
     w, _, _, n = tms.xy_bounds(ul_tile)
 
     # The output resolution should match the TMS resolution at MaxZoom
-    vrt_res = tms._resolution(tms.matrix(max_zoom))
+    vrt_res = tms.matrix(max_zoom).cellSize
 
     # Output transform is built from the origin (UL tile) and output resolution
     vrt_transform = Affine(vrt_res, 0, w, 0, -vrt_res, n)