diff --git a/sys/i386/i386/pmap.c b/sys/i386/i386/pmap.c
index a2a5b0d12ca0..38cc84c19f00 100644
--- a/sys/i386/i386/pmap.c
+++ b/sys/i386/i386/pmap.c
@@ -493,9 +493,13 @@ pmap_bootstrap(vm_paddr_t firstaddr)
 	virtual_avail = va;
 
 	/*
-	 * Leave in place an identity mapping (virt == phys) for the low 1 MB
-	 * physical memory region that is used by the ACPI wakeup code.  This
-	 * mapping must not have PG_G set. 
+	 * Finish removing the identity mapping (virt == phys) of low memory.
+	 * It was only used for 2 instructions in locore.  locore then
+	 * unmapped the first PTD to get some null pointer checks.  ACPI
+	 * wakeup will map the first PTD transiently to use it for 1
+	 * instruction.  The double mapping for low memory is not usable in
+	 * normal operation since it breaks trapping of null pointers and
+	 * causes inconsistencies in page tables when combined with PG_G.
 	 */
 	for (i = 1; i < NKPT; i++)
 		PTD[i] = 0;