diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
index b57e5f10f884..29e698006fac 100644
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -131,6 +131,7 @@ __FBSDID("$FreeBSD$");
 #include <vm/vm_extern.h>
 #include <vm/vm_pageout.h>
 #include <vm/vm_pager.h>
+#include <vm/vm_phys.h>
 #include <vm/vm_radix.h>
 #include <vm/vm_reserv.h>
 #include <vm/uma.h>
@@ -1056,8 +1057,7 @@ pmap_init(void)
 	/*
 	 * Calculate the size of the pv head table for superpages.
 	 */
-	for (i = 0; phys_avail[i + 1]; i += 2);
-	pv_npg = round_2mpage(phys_avail[(i - 2) + 1]) / NBPDR;
+	pv_npg = howmany(vm_phys_segs[vm_phys_nsegs - 1].end, NBPDR);
 
 	/*
 	 * Allocate memory for the pv head table for superpages.
diff --git a/sys/arm/arm/pmap-v6.c b/sys/arm/arm/pmap-v6.c
index c0d5a2ebf629..a913809517c0 100644
--- a/sys/arm/arm/pmap-v6.c
+++ b/sys/arm/arm/pmap-v6.c
@@ -172,6 +172,7 @@ __FBSDID("$FreeBSD$");
 #include <vm/vm_map.h>
 #include <vm/vm_page.h>
 #include <vm/vm_pageout.h>
+#include <vm/vm_phys.h>
 #include <vm/vm_extern.h>
 #include <vm/vm_reserv.h>
 
@@ -1342,9 +1343,10 @@ pmap_init(void)
 
 	/*
 	 * Calculate the size of the pv head table for superpages.
+	 * Handle the possibility that "vm_phys_segs[...].end" is zero.
 	 */
-	for (i = 0; phys_avail[i + 1]; i += 2);
-	pv_npg = round_1mpage(phys_avail[(i - 2) + 1]) / NBPDR;
+	pv_npg = trunc_1mpage(vm_phys_segs[vm_phys_nsegs - 1].end -
+	    PAGE_SIZE) / NBPDR + 1;
 
 	/*
 	 * Allocate memory for the pv head table for superpages.
diff --git a/sys/i386/i386/pmap.c b/sys/i386/i386/pmap.c
index 90ea046ad6e3..851372430e0f 100644
--- a/sys/i386/i386/pmap.c
+++ b/sys/i386/i386/pmap.c
@@ -133,6 +133,7 @@ __FBSDID("$FreeBSD$");
 #include <vm/vm_extern.h>
 #include <vm/vm_pageout.h>
 #include <vm/vm_pager.h>
+#include <vm/vm_phys.h>
 #include <vm/vm_radix.h>
 #include <vm/vm_reserv.h>
 #include <vm/uma.h>
@@ -778,9 +779,10 @@ pmap_init(void)
 
 	/*
 	 * Calculate the size of the pv head table for superpages.
+	 * Handle the possibility that "vm_phys_segs[...].end" is zero.
 	 */
-	for (i = 0; phys_avail[i + 1]; i += 2);
-	pv_npg = round_4mpage(phys_avail[(i - 2) + 1]) / NBPDR;
+	pv_npg = trunc_4mpage(vm_phys_segs[vm_phys_nsegs - 1].end -
+	    PAGE_SIZE) / NBPDR + 1;
 
 	/*
 	 * Allocate memory for the pv head table for superpages.