diff --git a/NodeGraphQt/base/graph.py b/NodeGraphQt/base/graph.py
index 5bed6341..0bfeadc5 100644
--- a/NodeGraphQt/base/graph.py
+++ b/NodeGraphQt/base/graph.py
@@ -907,7 +907,7 @@ def set_context_menu_from_file(self, file_path, menu='graph'):
         if not file.is_file():
             raise IOError('file doesn\'t exist: "{}"'.format(file))
 
-        with file.open() as f:
+        with file.open(encoding='utf8') as f:
             data = json.load(f)
         context_menu = self.get_context_menu(menu)
         self._deserialize_context_menu(context_menu, data, file)
@@ -1727,8 +1727,12 @@ def _serialize(self, nodes):
         serial_data['graph']['pipe_style'] = self.pipe_style()
 
         # connection constrains.
-        serial_data['graph']['accept_connection_types'] = self.model.accept_connection_types
-        serial_data['graph']['reject_connection_types'] = self.model.reject_connection_types
+        serial_data['graph']['accept_connection_types'] = {
+            k: list(v) for k, v in self.model.accept_connection_types.items()
+        }
+        serial_data['graph']['reject_connection_types'] = {
+            k: list(v) for k, v in self.model.reject_connection_types.items()
+        }
 
         # serialize nodes.
         for n in nodes:
@@ -1798,9 +1802,13 @@ def _deserialize(self, data, relative_pos=False, pos=None):
 
             # connection constrains.
             elif attr_name == 'accept_connection_types':
-                self.model.accept_connection_types = attr_value
+                self.model.accept_connection_types = {
+                    k: set(v) for k, v in attr_value.items()
+                }
             elif attr_name == 'reject_connection_types':
-                self.model.reject_connection_types = attr_value
+                self.model.reject_connection_types = {
+                    k: set(v) for k, v in attr_value.items()
+                }
 
         # build the nodes.
         nodes = {}
diff --git a/NodeGraphQt/base/model.py b/NodeGraphQt/base/model.py
index 8d1e8a37..e5896324 100644
--- a/NodeGraphQt/base/model.py
+++ b/NodeGraphQt/base/model.py
@@ -245,7 +245,7 @@ def add_port_accept_connection_type(
     ):
         """
         Convenience function for adding to the "accept_connection_types" dict.
-        If the node graph model is unavailable yet then we store it to a
+        If the node graph model is unavailable, yet then we store it to a
         temp var that gets deleted.
 
         Args:
diff --git a/NodeGraphQt/qgraphics/node_backdrop.py b/NodeGraphQt/qgraphics/node_backdrop.py
index 7696623d..6ff2236a 100644
--- a/NodeGraphQt/qgraphics/node_backdrop.py
+++ b/NodeGraphQt/qgraphics/node_backdrop.py
@@ -152,7 +152,7 @@ def mousePressEvent(self, event):
 
     def mouseReleaseEvent(self, event):
         super(BackdropNodeItem, self).mouseReleaseEvent(event)
-        self.setFlag(self.ItemIsMovable, True)
+        self.setFlag(QtWidgets.QGraphicsItem.ItemIsMovable, True)
         [n.setSelected(True) for n in self._nodes]
         self._nodes = [self]
 
diff --git a/NodeGraphQt/widgets/viewer.py b/NodeGraphQt/widgets/viewer.py
index 9de9bfbb..6aeeba3c 100644
--- a/NodeGraphQt/widgets/viewer.py
+++ b/NodeGraphQt/widgets/viewer.py
@@ -66,10 +66,9 @@ def __init__(self, parent=None, undo_stack=None):
         self.setRenderHint(QtGui.QPainter.Antialiasing, True)
         self.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
         self.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
-        self.setViewportUpdateMode(QtWidgets.QGraphicsView.FullViewportUpdate)
+        self.setViewportUpdateMode(QtWidgets.QGraphicsView.BoundingRectViewportUpdate)
         self.setCacheMode(QtWidgets.QGraphicsView.CacheBackground)
-        self.setOptimizationFlag(
-            QtWidgets.QGraphicsView.DontAdjustForAntialiasing)
+        self.setOptimizationFlag(QtWidgets.QGraphicsView.DontAdjustForAntialiasing)
 
         self.setAcceptDrops(True)
         self.resize(850, 800)
@@ -669,7 +668,11 @@ def wheelEvent(self, event):
             delta = event.angleDelta().y()
             if delta == 0:
                 delta = event.angleDelta().x()
-        self._set_viewer_zoom(delta, pos=event.pos())
+        try:
+            self._set_viewer_zoom(delta, pos=event.pos())
+        except AttributeError:
+            # For PyQt5 and above
+            self._set_viewer_zoom(delta, pos=event.position().toPoint())
 
     def dropEvent(self, event):
         pos = self.mapToScene(event.pos())