diff --git a/src/common/log.c b/src/common/log.c
index b533814844..bbad7f1dac 100644
--- a/src/common/log.c
+++ b/src/common/log.c
@@ -1246,7 +1246,7 @@ domain_to_string(log_domain_mask_t domain, char *buf, size_t buflen)
     const char *d;
     int bit = tor_log2(domain);
     size_t n;
-    if ((unsigned)bit >= sizeof(domain_list)/sizeof(*domain_list) - 1 ||
+    if ((unsigned)bit >= ARRAY_LENGTH(domain_list)-1 ||
         bit >= N_LOGGING_DOMAINS) {
       tor_snprintf(buf, buflen, "<BUG:Unknown domain %lx>", (long)domain);
       return buf+strlen(buf);