diff --git a/src/xpra/sound/pulseaudio/pulseaudio_common_util.py b/src/xpra/sound/pulseaudio/pulseaudio_common_util.py
index f73bbacc62..753426b79e 100755
--- a/src/xpra/sound/pulseaudio/pulseaudio_common_util.py
+++ b/src/xpra/sound/pulseaudio/pulseaudio_common_util.py
@@ -21,7 +21,7 @@ def get_x11_property(atom_name):
     try:
         from xpra.gtk_common.error import xswallow
         from xpra.x11.bindings.posix_display_source import X11DisplayContext    #@UnresolvedImport
-        from xpra.x11.bindings.window_bindings import X11WindowBindings
+        from xpra.x11.bindings.window_bindings import X11WindowBindingsInstance
     except ImportError as e:
         log("get_x11_property(%s)", atom_name, exc_info=True)
         log.error("Error: unable to query X11 property '%s':", atom_name)
@@ -30,7 +30,7 @@ def get_x11_property(atom_name):
     try:
         with X11DisplayContext(display) as dc:
             with xswallow:
-                X11Window = X11WindowBindings()
+                X11Window = X11WindowBindingsInstance()
                 root = X11Window.getDefaultRootWindow()
                 log("getDefaultRootWindow()=%#x", root)
                 try:
diff --git a/src/xpra/x11/bindings/core_bindings.pxd b/src/xpra/x11/bindings/core_bindings.pxd
index 78baa1dd67..83548a1a1b 100644
--- a/src/xpra/x11/bindings/core_bindings.pxd
+++ b/src/xpra/x11/bindings/core_bindings.pxd
@@ -12,7 +12,7 @@ cdef extern from "X11/Xlib.h":
         pass
     ctypedef CARD32 Atom
 
-cdef class _X11CoreBindings:
+cdef class X11CoreBindingsInstance:
     cdef Display * display
     cdef char * display_name
     cdef Atom xatom(self, str_or_int)
diff --git a/src/xpra/x11/bindings/core_bindings.pyx b/src/xpra/x11/bindings/core_bindings.pyx
index 913fa462c7..d3dfa74302 100644
--- a/src/xpra/x11/bindings/core_bindings.pyx
+++ b/src/xpra/x11/bindings/core_bindings.pyx
@@ -54,11 +54,11 @@ cdef extern from "X11/Xlib.h":
 from xpra.x11.bindings.display_source cimport get_display
 from xpra.x11.bindings.display_source import get_display_name
 
-cdef _X11CoreBindings singleton = None
+cdef X11CoreBindingsInstance singleton = None
 def X11CoreBindings():
     global singleton
     if singleton is None:
-        singleton = _X11CoreBindings()
+        singleton = X11CoreBindingsInstance()
     return singleton
 
 #for debugging, we can hook this function which will log the caller:
@@ -77,7 +77,7 @@ def set_context_check(fn):
     context_check = fn
 
 
-cdef class _X11CoreBindings:
+cdef class X11CoreBindingsInstance:
 
     def __cinit__(self):
         assert is_X11(), "cannot load X11 bindings with wayland under python3 / GTK3"
diff --git a/src/xpra/x11/bindings/keyboard_bindings.pyx b/src/xpra/x11/bindings/keyboard_bindings.pyx
index 0f54313142..2fe27be2ac 100644
--- a/src/xpra/x11/bindings/keyboard_bindings.pyx
+++ b/src/xpra/x11/bindings/keyboard_bindings.pyx
@@ -241,16 +241,16 @@ cdef s(const char *v):
 # to the original C xmodmap code
 
 
-from xpra.x11.bindings.core_bindings cimport _X11CoreBindings
+from xpra.x11.bindings.core_bindings cimport X11CoreBindingsInstance
 
-cdef _X11KeyboardBindings singleton = None
+cdef X11KeyboardBindingsInstance singleton = None
 def X11KeyboardBindings():
     global singleton
     if singleton is None:
-        singleton = _X11KeyboardBindings()
+        singleton = X11KeyboardBindingsInstance()
     return singleton
 
-cdef class _X11KeyboardBindings(_X11CoreBindings):
+cdef class X11KeyboardBindingsInstance(X11CoreBindingsInstance):
 
     cdef XModifierKeymap* work_keymap
     cdef int min_keycode
diff --git a/src/xpra/x11/bindings/posix_display_source.pyx b/src/xpra/x11/bindings/posix_display_source.pyx
index bbadd11c4a..2740a55584 100644
--- a/src/xpra/x11/bindings/posix_display_source.pyx
+++ b/src/xpra/x11/bindings/posix_display_source.pyx
@@ -1,6 +1,6 @@
 # This file is part of Xpra.
 # Copyright (C) 2008, 2009 Nathaniel Smith <njs@pobox.com>
-# Copyright (C) 2010-2018 Antoine Martin <antoine@xpra.org>
+# Copyright (C) 2010-2019 Antoine Martin <antoine@xpra.org>
 # Xpra is released under the terms of the GNU GPL v2, or, at your option, any
 # later version. See the file COPYING for details.
 
@@ -15,6 +15,7 @@ from xpra.x11.bindings.display_source cimport set_display, get_display
 from xpra.x11.bindings.display_source import set_display_name
 from libc.stdint cimport uintptr_t
 
+
 cdef extern from "X11/Xlib.h":
     ctypedef struct Display:
         pass
@@ -40,9 +41,9 @@ cdef do_init_posix_display_source(display_name):
 def close_display_source(uintptr_t ptr):
     assert ptr!=0, "invalid NULL display pointer"
     cdef Display * display = <Display *> ptr
-    cdef int v = XCloseDisplay(display)
     set_display(NULL)
     set_display_name("CLOSED")
+    cdef int v = XCloseDisplay(display)
     return v
 
 
diff --git a/src/xpra/x11/bindings/randr_bindings.pyx b/src/xpra/x11/bindings/randr_bindings.pyx
index d518cc7199..9570546e38 100644
--- a/src/xpra/x11/bindings/randr_bindings.pyx
+++ b/src/xpra/x11/bindings/randr_bindings.pyx
@@ -124,16 +124,16 @@ cdef extern from "X11/extensions/Xrandr.h":
 
     short XRRConfigCurrentRate(XRRScreenConfiguration *config)
 
-from xpra.x11.bindings.core_bindings cimport _X11CoreBindings
+from xpra.x11.bindings.core_bindings cimport X11CoreBindingsInstance
 
-cdef _RandRBindings singleton = None
+cdef RandRBindingsInstance singleton = None
 def RandRBindings():
     global singleton
     if singleton is None:
-        singleton = _RandRBindings()
+        singleton = RandRBindingsInstance()
     return singleton
 
-cdef class _RandRBindings(_X11CoreBindings):
+cdef class RandRBindingsInstance(X11CoreBindingsInstance):
 
     cdef int _has_randr
     cdef object _added_modes
diff --git a/src/xpra/x11/bindings/window_bindings.pyx b/src/xpra/x11/bindings/window_bindings.pyx
index d1581c6621..31f0b2096a 100644
--- a/src/xpra/x11/bindings/window_bindings.pyx
+++ b/src/xpra/x11/bindings/window_bindings.pyx
@@ -10,6 +10,8 @@ from __future__ import absolute_import
 
 import struct
 
+from libc.stdint cimport uintptr_t
+
 from xpra.gtk_common.error import XError
 from xpra.os_util import strtobytes
 
@@ -387,18 +389,18 @@ class PropertyOverflow(PropertyError):
     pass
 
 
-from xpra.x11.bindings.core_bindings cimport _X11CoreBindings
+from xpra.x11.bindings.core_bindings cimport X11CoreBindingsInstance
 
 cdef int CONFIGURE_GEOMETRY_MASK = CWX | CWY | CWWidth | CWHeight
 
-cdef _X11WindowBindings singleton = None
+cdef X11WindowBindingsInstance singleton = None
 def X11WindowBindings():
     global singleton
     if singleton is None:
-        singleton = _X11WindowBindings()
+        singleton = X11WindowBindingsInstance()
     return singleton
 
-cdef class _X11WindowBindings(_X11CoreBindings):
+cdef class X11WindowBindingsInstance(X11CoreBindingsInstance):
 
     cdef object has_xshape
 
@@ -435,6 +437,7 @@ cdef class _X11WindowBindings(_X11CoreBindings):
                                  % (extension, cmajor, cminor, major, minor))
 
     def getDefaultRootWindow(self):
+        assert self.display
         return XDefaultRootWindow(self.display)
 
 
diff --git a/src/xpra/x11/bindings/xi2_bindings.pyx b/src/xpra/x11/bindings/xi2_bindings.pyx
index 533ddb22a3..9c0037459e 100644
--- a/src/xpra/x11/bindings/xi2_bindings.pyx
+++ b/src/xpra/x11/bindings/xi2_bindings.pyx
@@ -315,16 +315,16 @@ CLASS_INFO = {
     }
 
 
-from xpra.x11.bindings.core_bindings cimport _X11CoreBindings
+from xpra.x11.bindings.core_bindings cimport X11CoreBindingsInstance
 
-cdef _X11XI2Bindings singleton = None
+cdef X11CoreBindingsInstance singleton = None
 def X11XI2Bindings():
     global singleton
     if singleton is None:
-        singleton = _X11XI2Bindings()
+        singleton = X11XI2BindingsInstance()
     return singleton
 
-cdef class _X11XI2Bindings(_X11CoreBindings):
+cdef class X11XI2BindingsInstance(X11CoreBindingsInstance):
 
     cdef int opcode
     cdef object events
diff --git a/src/xpra/x11/bindings/ximage.pyx b/src/xpra/x11/bindings/ximage.pyx
index d899e70a11..501016cfca 100644
--- a/src/xpra/x11/bindings/ximage.pyx
+++ b/src/xpra/x11/bindings/ximage.pyx
@@ -890,16 +890,16 @@ cdef window_pixmap_wrapper(Display *xdisplay, Window xwindow):
     pw.init(xdisplay, xwindow, width, height)
     return pw
 
-from xpra.x11.bindings.core_bindings cimport _X11CoreBindings
+from xpra.x11.bindings.core_bindings cimport X11CoreBindingsInstance
 
-cdef _XImageBindings singleton = None
+cdef XImageBindingsInstance singleton = None
 def XImageBindings():
     global singleton
     if singleton is None:
-        singleton = _XImageBindings()
+        singleton = XImageBindingsInstance()
     return singleton
 
-cdef class _XImageBindings(_X11CoreBindings):
+cdef class XImageBindingsInstance(X11CoreBindingsInstance):
     cdef int has_xshm
 
     def __cinit__(self):