diff --git a/src/include/lib/simplehash.h b/src/include/lib/simplehash.h
index f6cbcd8c176..60ab472540d 100644
--- a/src/include/lib/simplehash.h
+++ b/src/include/lib/simplehash.h
@@ -41,7 +41,7 @@
  *	  - SH_SCOPE - in which scope (e.g. extern, static inline) do function
  *		declarations reside
  *	  - SH_RAW_ALLOCATOR - if defined, memory contexts are not used; instead,
- *	    use this to allocate bytes
+ *	    use this to allocate bytes. The allocator must zero the returned space.
  *	  - SH_USE_NONDEFAULT_ALLOCATOR - if defined no element allocator functions
  *		are defined, so you can supply your own
  *	  The following parameters are only relevant when SH_DEFINE is defined: