diff --git a/include/wx/gtk/window.h b/include/wx/gtk/window.h
index dbc427553f..f9116d3d20 100644
--- a/include/wx/gtk/window.h
+++ b/include/wx/gtk/window.h
@@ -215,7 +215,6 @@ public:
     bool                 m_sizeSet:1;
     bool                 m_resizing:1;
     bool                 m_isRadioButton:1;     // faster than IS_KIND_OF
-    bool                 m_isListBox:1;         // faster than IS_KIND_OF
     bool                 m_isFrame:1;           // faster than IS_KIND_OF
     bool                 m_acceptsFocus:1;      // true if not static
     bool                 m_hasFocus:1;          // true if == FindFocus()
diff --git a/include/wx/gtk1/window.h b/include/wx/gtk1/window.h
index dbc427553f..f9116d3d20 100644
--- a/include/wx/gtk1/window.h
+++ b/include/wx/gtk1/window.h
@@ -215,7 +215,6 @@ public:
     bool                 m_sizeSet:1;
     bool                 m_resizing:1;
     bool                 m_isRadioButton:1;     // faster than IS_KIND_OF
-    bool                 m_isListBox:1;         // faster than IS_KIND_OF
     bool                 m_isFrame:1;           // faster than IS_KIND_OF
     bool                 m_acceptsFocus:1;      // true if not static
     bool                 m_hasFocus:1;          // true if == FindFocus()
diff --git a/src/gtk/listbox.cpp b/src/gtk/listbox.cpp
index 2f909c4a88..c63ba920e3 100644
--- a/src/gtk/listbox.cpp
+++ b/src/gtk/listbox.cpp
@@ -335,7 +335,6 @@ bool wxListBox::Create( wxWindow *parent, wxWindowID id,
 {
     m_needParent = TRUE;
     m_acceptsFocus = TRUE;
-    m_isListBox = TRUE;
     m_prevSelection = 0;  // or -1 ??
     m_blockEvent = FALSE;
 
diff --git a/src/gtk1/listbox.cpp b/src/gtk1/listbox.cpp
index 2f909c4a88..c63ba920e3 100644
--- a/src/gtk1/listbox.cpp
+++ b/src/gtk1/listbox.cpp
@@ -335,7 +335,6 @@ bool wxListBox::Create( wxWindow *parent, wxWindowID id,
 {
     m_needParent = TRUE;
     m_acceptsFocus = TRUE;
-    m_isListBox = TRUE;
     m_prevSelection = 0;  // or -1 ??
     m_blockEvent = FALSE;