diff --git a/libguile/threads.c b/libguile/threads.c
index 14a3d7d4e..38f9f689e 100644
--- a/libguile/threads.c
+++ b/libguile/threads.c
@@ -632,7 +632,9 @@ get_thread_stack_base ()
 }
 
 #elif HAVE_PTHREAD_GET_STACKADDR_NP
-/* This method for MacOS X.  */
+/* This method for MacOS X.
+   It'd be nice if there was some documentation on pthread_get_stackaddr_np,
+   but as of 2006 there's nothing obvious at apple.com.  */
 #define HAVE_GET_THREAD_STACK_BASE
 static SCM_STACKITEM *
 get_thread_stack_base ()