diff --git a/src/redis.h b/src/redis.h
index b16bb5b3..f5ef7d8c 100644
--- a/src/redis.h
+++ b/src/redis.h
@@ -582,6 +582,8 @@ typedef struct redisOpArray {
  * Global server state
  *----------------------------------------------------------------------------*/
 
+/* AIX defines hz to __hz, we don't use this define and in order to allow
+ * Redis build on AIX we need to undef it. */
 #ifdef _AIX
 #undef hz
 #endif