diff --git a/lib/hash.h b/lib/hash.h
index 4cb772e..a6dd531 100644
--- a/lib/hash.h
+++ b/lib/hash.h
@@ -41,7 +41,7 @@
   /* Hash backet. */
   struct hash_backet **index;
 
-  /* Hash table size. */
+  /* Hash table size. Must be power of 2 */
   unsigned int size;
 
   /* Key make function. */