diff --git a/src/charset.c b/src/charset.c
index 12e10e1..50ca617 100644
--- a/src/charset.c
+++ b/src/charset.c
@@ -35,6 +35,8 @@
 #define CT_ID_CHAR	0x20	/* flag: set for ID chars */
 #define CT_FNAME_CHAR	0x40	/* flag: set for file name chars */
 
+static int in_win_border(win_T *wp, colnr_T vcol);
+
 /*
  * Fill g_chartab[].  Also fills curbuf->b_chartab[] with flags for keyword
  * characters for current buffer.
@@ -1174,7 +1176,7 @@
  * Return TRUE if virtual column "vcol" is in the rightmost column of window
  * "wp".
  */
-    int
+    static int
 in_win_border(win_T *wp, colnr_T vcol)
 {
     int		width1;		/* width of first line (after line number) */