diff --git a/src/regexp.c b/src/regexp.c
index 8c1431d..805056e 100644
--- a/src/regexp.c
+++ b/src/regexp.c
@@ -202,7 +202,7 @@
 
     if ((*pp)[1] == ':')
     {
-	for (i = 0; i < (int)(sizeof(class_names) / sizeof(*class_names)); ++i)
+	for (i = 0; i < (int)ARRAY_LENGTH(class_names); ++i)
 	    if (STRNCMP(*pp + 2, class_names[i], STRLEN(class_names[i])) == 0)
 	    {
 		*pp += STRLEN(class_names[i]) + 2;