Index: sys/vm/vm_phys.c
===================================================================
--- sys/vm/vm_phys.c
+++ sys/vm/vm_phys.c
@@ -697,8 +697,9 @@
 {
 	int order;
 
-	KASSERT(((VM_PAGE_TO_PHYS(m) + npages * PAGE_SIZE) &
-	    ((PAGE_SIZE << fls(npages / 2)) - 1)) == 0,
+	KASSERT(npages == 0 ||
+	    ((VM_PAGE_TO_PHYS(m) + npages * PAGE_SIZE) &
+	    ((PAGE_SIZE << (fls(npages) - 1)) - 1)) == 0,
 	    ("vm_phys_enq_range: page %p and npages %u are misaligned",
 	    m, npages));
 	while (npages > 0) {