Index: lib/libc/sys/mmap.2
===================================================================
--- lib/libc/sys/mmap.2
+++ lib/libc/sys/mmap.2
@@ -338,13 +338,14 @@
 This option creates
 a memory region that grows to at most
 .Fa len
-bytes in size, starting from the stack top and growing down.
-The
-stack top is the starting address returned by the call, plus
+bytes less the guard size.
+The region starts from the stack top and grows down.
+The stack top is the starting address returned by the call, plus
 .Fa len
 bytes.
 The bottom of the stack at maximum growth is the starting
-address returned by the call.
+address returned by the call plus the guard size.
+The guard is located at the address returned by the call.
 .Pp
 Stacks created with
 .Dv MAP_STACK