--- a/gfx/public/nsThemeConstants.h
+++ b/gfx/public/nsThemeConstants.h
@@ -36,16 +36,19 @@
 #define NS_THEME_TOOLBAR_DUAL_BUTTON_DROPDOWN              15
 
 // A separator.  Can be horizontal or vertical.
 #define NS_THEME_TOOLBAR_SEPARATOR                         16
 
 // The gripper for a toolbar.
 #define NS_THEME_TOOLBAR_GRIPPER                           17
 
+// A splitter.  Can be horizontal or vertical.
+#define NS_THEME_SPLITTER                                  19
+
 // A status bar in a main application window.
 #define NS_THEME_STATUSBAR                                 21
 
 // A single pane of a status bar.
 #define NS_THEME_STATUSBAR_PANEL                           22
 
 // The resizer background area in a status bar 
 // for the resizer widget in the corner of a window.