diff --git a/client.cpp b/client.cpp
index 5ecd29efbc..00d6b26729 100644
--- a/client.cpp
+++ b/client.cpp
@@ -109,7 +109,7 @@ Client::Client()
     , shadeHoverTimer(NULL)
     , delayedMoveResizeTimer(NULL)
     , in_group(NULL)
-    , window_group(None)
+    , m_windowGroup(XCB_WINDOW_NONE)
     , tab_group(NULL)
     , in_layer(UnknownLayer)
     , ping_timer(NULL)
@@ -1973,13 +1973,13 @@ void Client::getWMHints()
 {
     XWMHints* hints = XGetWMHints(display(), window());
     input = true;
-    window_group = None;
+    m_windowGroup = XCB_WINDOW_NONE;
     urgency = false;
     if (hints) {
         if (hints->flags & InputHint)
             input = hints->input;
         if (hints->flags & WindowGroupHint)
-            window_group = hints->window_group;
+            m_windowGroup = hints->window_group;
         urgency = !!(hints->flags & UrgencyHint);   // Need boolean, it's a uint bitfield
         XFree((char*)hints);
     }
diff --git a/client.h b/client.h
index b346c785f8..994d6f242c 100644
--- a/client.h
+++ b/client.h
@@ -934,7 +934,7 @@ private:
     Colormap cmap;
     QString cap_normal, cap_iconic, cap_suffix, cap_deco;
     Group* in_group;
-    Window window_group;
+    xcb_window_t m_windowGroup;
     TabGroup* tab_group;
     Layer in_layer;
     QTimer* ping_timer;
diff --git a/group.cpp b/group.cpp
index 18b442eeeb..7d6f4562ce 100644
--- a/group.cpp
+++ b/group.cpp
@@ -955,15 +955,15 @@ void Client::checkGroup(Group* set_group, bool force)
             in_group = set_group;
             in_group->addMember(this);
         }
-    } else if (window_group != None) {
-        Group* new_group = workspace()->findGroup(window_group);
+    } else if (m_windowGroup != XCB_WINDOW_NONE) {
+        Group* new_group = workspace()->findGroup(m_windowGroup);
         if (transientFor() != NULL && transientFor()->group() != new_group) {
             // move the window to the right group (e.g. a dialog provided
             // by different app, but transient for this one, so make it part of that group)
             new_group = transientFor()->group();
         }
         if (new_group == NULL)   // doesn't exist yet
-            new_group = new Group(window_group);
+            new_group = new Group(m_windowGroup);
         if (new_group != in_group) {
             if (in_group != NULL)
                 in_group->removeMember(this);
@@ -1065,7 +1065,7 @@ void Client::changeClientLeaderGroup(Group* gr)
     if (transientFor() != NULL)
         return;
     // also don't change the group for window which have group set
-    if (window_group)
+    if (m_windowGroup)
         return;
     checkGroup(gr);   // change group
 }