diff --git a/src/t_zset.c b/src/t_zset.c
index fe65bf756..d2535c727 100644
--- a/src/t_zset.c
+++ b/src/t_zset.c
@@ -64,6 +64,10 @@ void zslFree(zskiplist *zsl) {
     zfree(zsl);
 }
 
+/* Returns a random level for the new skiplist node we are going to create.
+ * The return value of this function is between 1 and ZSKIPLIST_MAXLEVEL
+ * (both inclusive), with a powerlaw-alike distribution where higher
+ * levels are less likely to be returned. */
 int zslRandomLevel(void) {
     int level = 1;
     while ((random()&0xFFFF) < (ZSKIPLIST_P * 0xFFFF))