diff --git a/src/vim.h b/src/vim.h
index fb991dc..d573cea 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -2334,4 +2334,7 @@
 #define DIP_OPT	    0x10	/* also use "opt" directory in 'packpath' */
 #define DIP_NORTP   0x20	/* do not use 'runtimepath' */
 
+/* Lowest number used for window ID. Cannot have this many windows. */
+#define LOWEST_WIN_ID 1000
+
 #endif /* VIM__H */