diff --git a/src/command_func.h b/src/command_func.h
--- a/src/command_func.h
+++ b/src/command_func.h
@@ -57,7 +57,6 @@ void NetworkSend_Command(TileIndex tile,
 #endif /* ENABLE_NETWORK */
 
 extern Money _additional_cash_required;
-extern StringID _error_message;
 
 /**
  * Checks if a integer value belongs to a command.