diff --git a/docs/releases/upcoming/1674.bugfix.rst b/docs/releases/upcoming/1674.bugfix.rst
new file mode 100644
index 000000000..1183d8ef5
--- /dev/null
+++ b/docs/releases/upcoming/1674.bugfix.rst
@@ -0,0 +1 @@
+Call HasPrivateTraits.__init__() in GroupEditor.__init__ (#1674)
\ No newline at end of file
diff --git a/traitsui/qt4/ui_panel.py b/traitsui/qt4/ui_panel.py
index 683b0fbe4..18ef6b870 100644
--- a/traitsui/qt4/ui_panel.py
+++ b/traitsui/qt4/ui_panel.py
@@ -28,7 +28,7 @@
 
 from pyface.qt import QtCore, QtGui
 
-from traits.api import Any, Instance, Undefined
+from traits.api import Any, HasPrivateTraits, Instance, Undefined
 from traits.observation.api import match
 
 from traitsui.api import Group
@@ -1259,6 +1259,10 @@ class GroupEditor(Editor):
     def __init__(self, **traits):
         """ Initialise the object.
         """
+        # We intentionally don't want to call Editor.__init__ here as
+        # GroupEditor does its own thing. However, we still want Traits
+        # machinery to be set up properly.
+        HasPrivateTraits.__init__(self, **traits)
         self.trait_set(**traits)