diff --git a/erlang.html.markdown b/erlang.html.markdown
index a897755e..e5db6423 100644
--- a/erlang.html.markdown
+++ b/erlang.html.markdown
@@ -172,7 +172,10 @@ is_pet(A)                                             -> false.
 
 % Warning: not all valid Erlang expressions can be used as guard expressions;
 % in particular, our `is_cat` and `is_dog` functions cannot be used within the
-% guard sequence in `is_pet`'s definition.
+% guard sequence in `is_pet`'s definition. For a list of the built-in
+% functions (BIFs) allowed in guard sequences, refer to this
+% [section](http://erlang.org/doc/reference_manual/expressions.html#id81912)
+% of the Erlang reference manual.
 
 % Records provide a method for associating a name with a particular element in a
 % tuple.