--- a/src/misc1.c
+++ b/src/misc1.c
@@ -671,7 +671,7 @@ open_line(dir, flags, old_indent)
 	    ptr = saved_line;
 # ifdef FEAT_COMMENTS
 	    if (flags & OPENLINE_DO_COM)
-		lead_len = get_leader_len(ptr, NULL, FALSE);
+		lead_len = get_leader_len(ptr, NULL, FALSE, TRUE);
 	    else
 		lead_len = 0;
 # endif
@@ -693,7 +693,7 @@ open_line(dir, flags, old_indent)
 		}
 # ifdef FEAT_COMMENTS
 		if (flags & OPENLINE_DO_COM)
-		    lead_len = get_leader_len(ptr, NULL, FALSE);
+		    lead_len = get_leader_len(ptr, NULL, FALSE, TRUE);
 		else
 		    lead_len = 0;
 		if (lead_len > 0)
@@ -836,7 +836,7 @@ open_line(dir, flags, old_indent)
      */
     end_comment_pending = NUL;
     if (flags & OPENLINE_DO_COM)
-	lead_len = get_leader_len(saved_line, &lead_flags, dir == BACKWARD);
+	lead_len = get_leader_len(saved_line, &lead_flags, dir == BACKWARD, TRUE);
     else
 	lead_len = 0;
     if (lead_len > 0)
@@ -1548,14 +1548,18 @@ theend:
  * When "flags" is not NULL, it is set to point to the flags of the recognized
  * comment leader.
  * "backward" must be true for the "O" command.
+ * If "include_space" is set, include trailing whitespace while calculating the
+ * length.
  */
     int
-get_leader_len(line, flags, backward)
+get_leader_len(line, flags, backward, include_space)
     char_u	*line;
     char_u	**flags;
     int		backward;
+    int		include_space;
 {
     int		i, j;
+    int		result;
     int		got_com = FALSE;
     int		found_one;
     char_u	part_buf[COM_MAX_LEN];	/* buffer for one option part */
@@ -1565,7 +1569,7 @@ get_leader_len(line, flags, backward)
     char_u	*prev_list;
     char_u	*saved_flags = NULL;
 
-    i = 0;
+    result = i = 0;
     while (vim_iswhite(line[i]))    /* leading white space is ignored */
 	++i;
 
@@ -1668,17 +1672,167 @@ get_leader_len(line, flags, backward)
 	if (!found_one)
 	    break;
 
+	result = i;
+
 	/* Include any trailing white space. */
 	while (vim_iswhite(line[i]))
 	    ++i;
 
+	if (include_space)
+	    result = i;
+
 	/* If this comment doesn't nest, stop here. */
 	got_com = TRUE;
 	if (vim_strchr(part_buf, COM_NEST) == NULL)
 	    break;
     }
-
-    return (got_com ? i : 0);
+    return result;
+}
+
+/*
+ * Return the offset at which the last comment in line starts. If there is no
+ * comment in the whole line, -1 is returned.
+ *
+ * When "flags" is not null, it is set to point to the flags describing the
+ * recognized comment leader.
+ */
+    int
+get_last_leader_offset(line, flags)
+    char_u	*line;
+    char_u	**flags;
+{
+    int		result = -1;
+    int		i, j;
+    int		lower_check_bound = 0;
+    char_u	*string;
+    char_u	*com_leader;
+    char_u	*com_flags;
+    char_u	*list;
+    int		found_one;
+    char_u	part_buf[COM_MAX_LEN];	/* buffer for one option part */
+
+    /*
+     * Repeat to match several nested comment strings.
+     */
+    i = (int)STRLEN(line);
+    while (--i >= lower_check_bound)
+    {
+	/*
+	 * scan through the 'comments' option for a match
+	 */
+	found_one = FALSE;
+	for (list = curbuf->b_p_com; *list; )
+	{
+	    char_u *flags_save = list;
+
+	    /*
+	     * Get one option part into part_buf[].  Advance list to next one.
+	     * put string at start of string.
+	     */
+	    (void)copy_option_part(&list, part_buf, COM_MAX_LEN, ",");
+	    string = vim_strchr(part_buf, ':');
+	    if (string == NULL)	/* If everything is fine, this cannot actually
+				 * happen. */
+	    {
+		continue;
+	    }
+	    *string++ = NUL;	/* Isolate flags from string. */
+	    com_leader = string;
+
+	    /*
+	     * Line contents and string must match.
+	     * When string starts with white space, must have some white space
+	     * (but the amount does not need to match, there might be a mix of
+	     * TABs and spaces).
+	     */
+	    if (vim_iswhite(string[0]))
+	    {
+		if (i == 0 || !vim_iswhite(line[i - 1]))
+		    continue;
+		while (vim_iswhite(string[0]))
+		    ++string;
+	    }
+	    for (j = 0; string[j] != NUL && string[j] == line[i + j]; ++j)
+		/* do nothing */;
+	    if (string[j] != NUL)
+		continue;
+
+	    /*
+	     * When 'b' flag used, there must be white space or an
+	     * end-of-line after the string in the line.
+	     */
+	    if (vim_strchr(part_buf, COM_BLANK) != NULL
+		    && !vim_iswhite(line[i + j]) && line[i + j] != NUL)
+	    {
+		continue;
+	    }
+
+	    /*
+	     * We have found a match, stop searching.
+	     */
+	    found_one = TRUE;
+
+	    if (flags)
+		*flags = flags_save;
+	    com_flags = flags_save;
+
+	    break;
+	}
+
+	if (found_one)
+	{
+	    char_u  part_buf2[COM_MAX_LEN];	/* buffer for one option part */
+	    int     len1, len2, off;
+
+	    result = i;
+	    /*
+	     * If this comment nests, continue searching.
+	     */
+	    if (vim_strchr(part_buf, COM_NEST) != NULL)
+		continue;
+
+	    lower_check_bound = i;
+
+	    /* Let's verify whether the comment leader found is a substring
+	     * of other comment leaders. If it is, let's adjust the
+	     * lower_check_bound so that we make sure that we have determined
+	     * the comment leader correctly.
+	     */
+
+	    while (vim_iswhite(*com_leader))
+		++com_leader;
+	    len1 = (int)STRLEN(com_leader);
+
+	    for (list = curbuf->b_p_com; *list; )
+	    {
+		char_u *flags_save = list;
+
+		(void)copy_option_part(&list, part_buf2, COM_MAX_LEN, ",");
+		if (flags_save == com_flags)
+		    continue;
+		string = vim_strchr(part_buf2, ':');
+		++string;
+		while (vim_iswhite(*string))
+		    ++string;
+		len2 = (int)STRLEN(string);
+		if (len2 == 0)
+		    continue;
+
+		/* Now we have to verify whether string ends with a substring
+		 * beginning the com_leader. */
+		for (off = (len2 > i ? i : len2); off > 0 && off + len1 > len2;)
+		{
+		    --off;
+		    if (!STRNCMP(string + off, com_leader, len2 - off))
+		    {
+			if (i - off < lower_check_bound)
+			    lower_check_bound = i - off;
+		    }
+		}
+	    }
+	}
+    }
+    return result;
 }
 #endif