diff --git a/Include/WinMessages.nsh b/Include/WinMessages.nsh
index 19a2254c..34bb145e 100644
--- a/Include/WinMessages.nsh
+++ b/Include/WinMessages.nsh
@@ -135,6 +135,8 @@ UDM     Up-down control
 !define CB_SETTOPINDEX              0x015c
 !define CB_SHOWDROPDOWN             0x014F
 
+!define CB_ERR                      -1
+
 #Edit Control Messages#
 !define EM_CANUNDO              0x00C6
 !define EM_CHARFROMPOS          0x00D7
@@ -220,6 +222,8 @@ UDM     Up-down control
 !define LB_SETTABSTOPS          0x0192
 !define LB_SETTOPINDEX          0x0197
 
+!define LB_ERR                  -1
+
 #Window Messages#
 !define WM_ACTIVATE                     0x0006
 !define WM_ACTIVATEAPP                  0x001C