diff --git a/invesalius/data/geometry.py b/invesalius/data/geometry.py
index 27cc93b..ba2543c 100644
--- a/invesalius/data/geometry.py
+++ b/invesalius/data/geometry.py
@@ -22,14 +22,13 @@ import math
 
 import numpy as np
 import vtk
-from six import with_metaclass
 from pubsub import pub as Publisher
 
 import invesalius.constants as const
 import invesalius.utils as utils
 
 
-class Box(with_metaclass(utils.Singleton, object)):
+class Box(metaclass=utils.Singleton):
     """
     This class is a data structure for storing the
     coordinates (min and max) of box used in crop-mask.
diff --git a/invesalius/data/measures.py b/invesalius/data/measures.py
index 48397aa..d0250bd 100644
--- a/invesalius/data/measures.py
+++ b/invesalius/data/measures.py
@@ -1,7 +1,5 @@
 # -*- coding: UTF-8 -*-
 
-from six import with_metaclass
-
 import math
 import random
 import sys
@@ -57,7 +55,7 @@ else:
 
 DEBUG_DENSITY = False
 
-class MeasureData(with_metaclass(utils.Singleton)):
+class MeasureData(metaclass=utils.Singleton):
     """
     Responsible to keep measures data.
     """
diff --git a/invesalius/data/slice_.py b/invesalius/data/slice_.py
index bb2bfbf..86d7d5b 100644
--- a/invesalius/data/slice_.py
+++ b/invesalius/data/slice_.py
@@ -22,7 +22,6 @@ import tempfile
 import numpy as np
 import vtk
 from scipy import ndimage
-from six import with_metaclass
 from pubsub import pub as Publisher
 
 import invesalius.constants as const
@@ -77,7 +76,7 @@ class SliceBuffer(object):
 # Only one slice will be initialized per time (despite several viewers
 # show it from distinct perspectives).
 # Therefore, we use Singleton design pattern for implementing it.
-class Slice(with_metaclass(utils.Singleton, object)):
+class Slice(metaclass=utils.Singleton):
     def __init__(self):
         self.current_mask = None
         self.blend_filter = None
diff --git a/invesalius/data/styles.py b/invesalius/data/styles.py
index 7f7a72d..248715b 100644
--- a/invesalius/data/styles.py
+++ b/invesalius/data/styles.py
@@ -30,7 +30,6 @@ import wx
 from scipy import ndimage
 from imageio import imsave
 from scipy.ndimage import generate_binary_structure, watershed_ift
-from six import with_metaclass
 from skimage.morphology import watershed
 from pubsub import pub as Publisher
 
@@ -1127,7 +1126,7 @@ class ChangeSliceInteractorStyle(DefaultInteractorStyle):
         self.last_position = position[1]
 
 
-class EditorConfig(with_metaclass(utils.Singleton, object)):
+class EditorConfig(metaclass=utils.Singleton):
     def __init__(self):
         self.operation = const.BRUSH_THRESH
         self.cursor_type = const.BRUSH_CIRCLE
@@ -1394,7 +1393,7 @@ class WatershedProgressWindow(object):
         self.dlg.Destroy()
 
 
-class WatershedConfig(with_metaclass(utils.Singleton, object)):
+class WatershedConfig(metaclass=utils.Singleton):
     def __init__(self):
         self.algorithm = "Watershed"
         self.con_2d = 4
@@ -2174,7 +2173,7 @@ class ReorientImageInteractorStyle(DefaultInteractorStyle):
             buffer_.discard_image()
 
 
-class FFillConfig(with_metaclass(utils.Singleton, object)):
+class FFillConfig(metaclass=utils.Singleton):
     def __init__(self):
         self.dlg_visible = False
         self.target = "2D"
@@ -2310,7 +2309,7 @@ class RemoveMaskPartsInteractorStyle(FloodFillMaskInteractorStyle):
         self._progr_title = _(u"Remove part")
         self._progr_msg = _(u"Removing part ...")
 
-class CropMaskConfig(with_metaclass(utils.Singleton, object)):
+class CropMaskConfig(metaclass=utils.Singleton):
     def __init__(self):
         self.dlg_visible = False
 
@@ -2411,7 +2410,7 @@ class CropMaskInteractorStyle(DefaultInteractorStyle):
             Publisher.sendMessage('Reload actual slice')
 
 
-class SelectPartConfig(with_metaclass(utils.Singleton, object)):
+class SelectPartConfig(metaclass=utils.Singleton):
     def __init__(self):
         self.mask = None
         self.con_3d = 6
@@ -2517,7 +2516,7 @@ class SelectMaskPartsInteractorStyle(DefaultInteractorStyle):
         self.config.mask = mask
 
 
-class FFillSegmentationConfig(with_metaclass(utils.Singleton, object)):
+class FFillSegmentationConfig(metaclass=utils.Singleton):
     def __init__(self):
         self.dlg_visible = False
         self.target = "2D"
diff --git a/invesalius/project.py b/invesalius/project.py
index 60fd275..2f79620 100644
--- a/invesalius/project.py
+++ b/invesalius/project.py
@@ -29,7 +29,6 @@ import tempfile
 import numpy as np
 import vtk
 import wx
-from six import with_metaclass
 
 from pubsub import pub as Publisher
 
@@ -52,7 +51,7 @@ else:
 
 # Only one project will be initialized per time. Therefore, we use
 # Singleton design pattern for implementing it
-class Project(with_metaclass(Singleton, object)):
+class Project(metaclass=Singleton):
     def __init__(self):
         # Patient/ acquistion information
         self.name = ''
diff --git a/invesalius/session.py b/invesalius/session.py
index e5465ad..9c9901d 100644
--- a/invesalius/session.py
+++ b/invesalius/session.py
@@ -17,8 +17,6 @@
 #    detalhes.
 #--------------------------------------------------------------------------
 
-from six import with_metaclass
-
 try:
     import configparser as ConfigParser
 except(ImportError):
@@ -51,7 +49,7 @@ SESSION_ENCODING = 'utf8'
 
 # Only one session will be initialized per time. Therefore, we use
 # Singleton design pattern for implementing it
-class Session(with_metaclass(Singleton, object)):
+class Session(metaclass=Singleton):
 
     def __init__(self):
         self.project_path = ()
--
libgit2 0.21.2