diff --git a/mozilla/widget/src/xlib/nsKeyCode.cpp b/mozilla/widget/src/xlib/nsKeyCode.cpp
index ec24ac9dfdb..d0babc09af3 100644
--- a/mozilla/widget/src/xlib/nsKeyCode.cpp
+++ b/mozilla/widget/src/xlib/nsKeyCode.cpp
@@ -36,7 +36,9 @@ struct nsKeyConverter nsKeycodes[] =
   { NS_VK_CANCEL,        XK_Cancel},
   { NS_VK_BACK,          XK_BackSpace},
   { NS_VK_TAB,           XK_Tab},
-  { NS_VK_TAB,           XK_ISO_Left_Tab },    
+#ifdef XK_ISO_Left_Tab
+  { NS_VK_TAB,           XK_ISO_Left_Tab }, // SunOS 5.5.1 doesn't have it.
+#endif
   { NS_VK_CLEAR,         XK_Clear},
   { NS_VK_RETURN,        XK_Return},
   { NS_VK_ENTER,         XK_KP_Enter},