diff --git a/sys/vm/vm_pageout.c b/sys/vm/vm_pageout.c
index 762b293e0704..90ab28870611 100644
--- a/sys/vm/vm_pageout.c
+++ b/sys/vm/vm_pageout.c
@@ -372,10 +372,13 @@ vm_pageout_flush(mc, count, flags)
 	 *
 	 * We do not have to fixup the clean/dirty bits here... we can
 	 * allow the pager to do it after the I/O completes.
+	 *
+	 * NOTE! mc[i]->dirty may be partial or fragmented due to an
+	 * edge case with file fragments.
 	 */
 
 	for (i = 0; i < count; i++) {
-		KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL && mc[i]->dirty == VM_PAGE_BITS_ALL, ("vm_pageout_flush page %p index %d/%d: partially dirty page", mc[i], i, count));
+		KASSERT(mc[i]->valid == VM_PAGE_BITS_ALL, ("vm_pageout_flush page %p index %d/%d: partially invalid page", mc[i], i, count));
 		vm_page_io_start(mc[i]);
 		vm_page_protect(mc[i], VM_PROT_READ);
 	}