diff --git a/src/eval.c b/src/eval.c
index 22779e3..e9ab035 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -23205,6 +23205,7 @@
     int		c;
     int		has_fullname = 0;
 #ifdef WIN3264
+    char_u	*fname_start = *fnamep;
     int		has_shortname = 0;
 #endif
 
@@ -23379,24 +23380,25 @@
     }
 
 #ifdef WIN3264
-    /* Check shortname after we have done 'heads' and before we do 'tails'
+    /*
+     * Handle ":8" after we have done 'heads' and before we do 'tails'.
      */
     if (has_shortname)
     {
-	pbuf = NULL;
-	/* Copy the string if it is shortened by :h */
-	if (*fnamelen < (int)STRLEN(*fnamep))
+	/* Copy the string if it is shortened by :h and when it wasn't copied
+	 * yet, because we are going to change it in place.  Avoids changing
+	 * the buffer name for "%:8". */
+	if (*fnamelen < (int)STRLEN(*fnamep) || *fnamep == fname_start)
 	{
 	    p = vim_strnsave(*fnamep, *fnamelen);
-	    if (p == 0)
+	    if (p == NULL)
 		return -1;
 	    vim_free(*bufp);
 	    *bufp = *fnamep = p;
 	}
 
 	/* Split into two implementations - makes it easier.  First is where
-	 * there isn't a full name already, second is where there is.
-	 */
+	 * there isn't a full name already, second is where there is. */
 	if (!has_fullname && !vim_isAbsName(*fnamep))
 	{
 	    if (shortpath_for_partial(fnamep, bufp, fnamelen) == FAIL)
@@ -23404,18 +23406,16 @@
 	}
 	else
 	{
-	    int		l;
+	    int		l = *fnamelen;
 
-	    /* Simple case, already have the full-name
+	    /* Simple case, already have the full-name.
 	     * Nearly always shorter, so try first time. */
-	    l = *fnamelen;
 	    if (get_short_pathname(fnamep, bufp, &l) == FAIL)
 		return -1;
 
 	    if (l == 0)
 	    {
-		/* Couldn't find the filename.. search the paths.
-		 */
+		/* Couldn't find the filename, search the paths. */
 		l = *fnamelen;
 		if (shortpath_for_invalid_fname(fnamep, bufp, &l) == FAIL)
 		    return -1;