diff --git a/common.c b/common.c
index 95590f5..94d5aa4 100644
--- a/common.c
+++ b/common.c
@@ -58,6 +58,13 @@
 		(link)->next = (following);                                            \
 	BLOCK_END
 
+static void
+transform_str (char *s, int (*tolower) (int c))
+{
+	for (; *s; s++)
+		*s = tolower (*s);
+}
+
 static void
 split_str (const char *s, char delimiter, struct str_vector *out)
 {
diff --git a/degesch.c b/degesch.c
index 6c8d1f5..6294316 100644
--- a/degesch.c
+++ b/degesch.c
@@ -4413,12 +4413,10 @@ irc_is_highlight (struct server *s, const char *message)
 	// Well, this is rather crude but it should make most users happy.
 	// Ideally we could do this at least in proper Unicode.
 	char *copy = xstrdup (message);
-	for (char *p = copy; *p; p++)
-		*p = s->irc_tolower (*p);
+	transform_str (copy, s->irc_tolower);
 
 	char *nick = xstrdup (s->irc_user->nickname);
-	for (char *p = nick; *p; p++)
-		*p = s->irc_tolower (*p);
+	transform_str (nick, s->irc_tolower);
 
 	// Special characters allowed in nicknames by RFC 2812: []\`_^{|} and -
 	// Also excluded from the ASCII: common user channel prefixes: +%@&~
@@ -6825,8 +6823,7 @@ handle_command_ctcp (struct handler_args *a)
 		return false;
 
 	char *tag = cut_word (&a->arguments);
-	for (char *p = tag; *p; p++)
-		*p = toupper_ascii (*p);
+	transform_str (tag, toupper_ascii);
 
 	if (*a->arguments)
 		irc_send (a->s, "PRIVMSG %s :\x01%s %s\x01", target, tag, a->arguments);