diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 4c22b3d9..0739287a 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -6,6 +6,12 @@ All notable changes to this project will be documented in this file.
 The format is based on `Keep a Changelog`_,
 and this project adheres to `Semantic Versioning`_.
 
+`1.5.6`_ - 2022-09-01
+--------------------------
+Fixed
+'''''''
+- Bug in RasterMesh VTK writer.
+
 `1.5.5`_ - 2022-08-31
 --------------------------
 Changed
@@ -286,7 +292,8 @@ Added
 
 .. LINKS
 
-.. _`Unreleased`: https://github.com/kip-hart/MicroStructPy/compare/v1.5.5...HEAD
+.. _`Unreleased`: https://github.com/kip-hart/MicroStructPy/compare/v1.5.6...HEAD
+.. _`1.5.6`: https://github.com/kip-hart/MicroStructPy/compare/v1.5.5...v1.5.6
 .. _`1.5.5`: https://github.com/kip-hart/MicroStructPy/compare/v1.5.4...v1.5.5
 .. _`1.5.4`: https://github.com/kip-hart/MicroStructPy/compare/v1.5.3...v1.5.4
 .. _`1.5.3`: https://github.com/kip-hart/MicroStructPy/compare/v1.5.2...v1.5.3
diff --git a/setup.py b/setup.py
index 0bea467d..aaf2b622 100644
--- a/setup.py
+++ b/setup.py
@@ -79,7 +79,7 @@ def find_version(*fname):
         'aabbtree>=2.5.0',
         'pybind11',  # must come before meshpy for successful install
         'lsq-ellipse',
-        'matplotlib>=3.0.0',
+        'matplotlib>=3.3.0',
         'meshpy>=2018.2.1',
         'numpy>=1.13.0',
         'pygmsh>=7.0.2',
diff --git a/src/microstructpy/__init__.py b/src/microstructpy/__init__.py
index 00812160..ec8a5777 100644
--- a/src/microstructpy/__init__.py
+++ b/src/microstructpy/__init__.py
@@ -4,4 +4,4 @@
 import microstructpy.seeding
 import microstructpy.verification
 
-__version__ = '1.5.5'
+__version__ = '1.5.6'
diff --git a/src/microstructpy/meshing/trimesh.py b/src/microstructpy/meshing/trimesh.py
index a6c77ca6..4ac4467d 100644
--- a/src/microstructpy/meshing/trimesh.py
+++ b/src/microstructpy/meshing/trimesh.py
@@ -1170,7 +1170,8 @@ def write(self, filename, format='txt', seeds=None, polymesh=None):
             pt_fmt = '{: f} {: f} {: f}\n'
 
             # Dimensions
-            coords = [list(set(ax)) for ax in zip(*self.points)]
+            pts = np.array(self.points)
+            coords = [np.unique(ax) for ax in pts.T]
             if len(coords) < 3:
                 coords.append([0])  # force z=0 for 2D meshes
             dims = [len(c) for c in coords]