diff --git a/sys/kern/subr_physmem.c b/sys/kern/subr_physmem.c
--- a/sys/kern/subr_physmem.c
+++ b/sys/kern/subr_physmem.c
@@ -180,7 +180,7 @@
     uint64_t maxphyssz, long *pavail, long *prealmem)
 {
 	size_t acnt, exi, hwi;
-	uint64_t end, start, xend, xstart;
+	uint64_t adj, end, start, xend, xstart;
 	long availmem, totalmem;
 	const struct region *exp, *hwp;
 	uint64_t availsz;
@@ -190,8 +190,9 @@
 	availsz = 0;
 	acnt = 0;
 	for (hwi = 0, hwp = hwregions; hwi < hwcnt; ++hwi, ++hwp) {
-		start = hwp->addr;
-		end   = hwp->size + start;
+		adj   = round_page(hwp->addr) - hwp->addr;
+		start = round_page(hwp->addr);
+		end   = trunc_page(hwp->size + adj) + start;
 		totalmem += atop((vm_offset_t)(end - start));
 		for (exi = 0, exp = exregions; exi < excnt; ++exi, ++exp) {
 			/*
@@ -417,8 +418,6 @@
 void
 physmem_hardware_region(uint64_t pa, uint64_t sz)
 {
-	vm_offset_t adj;
-
 	/*
 	 * Filter out the page at PA 0x00000000.  The VM can't handle it, as
 	 * pmap_extract() == 0 means failure.
@@ -451,14 +450,6 @@
 		sz -= 1024 * 1024;
 	}
 
-	/*
-	 * Round the starting address up to a page boundary, and truncate the
-	 * ending page down to a page boundary.
-	 */
-	adj = round_page(pa) - pa;
-	pa  = round_page(pa);
-	sz  = trunc_page(sz - adj);
-
 	if (sz > 0 && hwcnt < nitems(hwregions))
 		hwcnt = insert_region(hwregions, hwcnt, pa, sz, 0);
 }
diff --git a/tests/sys/kern/subr_physmem_test.c b/tests/sys/kern/subr_physmem_test.c
--- a/tests/sys/kern/subr_physmem_test.c
+++ b/tests/sys/kern/subr_physmem_test.c
@@ -76,14 +76,12 @@
 	ATF_CHECK_EQ(avail[0], 2 * PAGE_SIZE);
 	ATF_CHECK_EQ(avail[1], 6 * PAGE_SIZE);
 
-#ifdef notyet /* This doesn't currently work */
 	/* Add the remaining part of the page */
 	physmem_hardware_region(6 * PAGE_SIZE + PAGE_SIZE / 2, PAGE_SIZE / 2);
 	len = physmem_avail(avail, 4);
 	ATF_CHECK_EQ(len, 2);
 	ATF_CHECK_EQ(avail[0], 2 * PAGE_SIZE);
 	ATF_CHECK_EQ(avail[1], 7 * PAGE_SIZE);
-#endif
 }
 
 ATF_TC_WITHOUT_HEAD(hwregion_exclude);
@@ -113,10 +111,30 @@
 	ATF_CHECK_EQ(avail[3], 7 * PAGE_SIZE);
 }
 
+ATF_TC_WITHOUT_HEAD(hwregion_unordered);
+ATF_TC_BODY(hwregion_unordered, tc)
+{
+	vm_paddr_t avail[4];
+	size_t len;
+
+	/* Add a partial page */
+	physmem_hardware_region(PAGE_SIZE, PAGE_SIZE / 2);
+	/* Add a full page not touching the previous */
+	physmem_hardware_region( 2 * PAGE_SIZE, PAGE_SIZE);
+	/* Add the remainder of the first page */
+	physmem_hardware_region(PAGE_SIZE + PAGE_SIZE / 2, PAGE_SIZE / 2);
+
+	len = physmem_avail(avail, 4);
+	ATF_CHECK_EQ(len, 2);
+	ATF_CHECK_EQ(avail[0], PAGE_SIZE);
+	ATF_CHECK_EQ(avail[1], 3 * PAGE_SIZE);
+}
+
 ATF_TP_ADD_TCS(tp)
 {
 
 	ATF_TP_ADD_TC(tp, hwregion);
 	ATF_TP_ADD_TC(tp, hwregion_exclude);
+	ATF_TP_ADD_TC(tp, hwregion_unordered);
 	return (atf_no_error());
 }