diff --git a/block/mirror.c b/block/mirror.c
index 21f2d8d..6e502e3 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -259,9 +259,11 @@
     next_sector = sector_num;
     while (nb_chunks-- > 0) {
         MirrorBuffer *buf = QSIMPLEQ_FIRST(&s->buf_free);
+        size_t remaining = (nb_sectors * BDRV_SECTOR_SIZE) - op->qiov.size;
+
         QSIMPLEQ_REMOVE_HEAD(&s->buf_free, next);
         s->buf_free_count--;
-        qemu_iovec_add(&op->qiov, buf, s->granularity);
+        qemu_iovec_add(&op->qiov, buf, MIN(s->granularity, remaining));
 
         /* Advance the HBitmapIter in parallel, so that we do not examine
          * the same sector twice.
diff --git a/tests/qemu-iotests/041 b/tests/qemu-iotests/041
index ef4f465..ef74be6 100755
--- a/tests/qemu-iotests/041
+++ b/tests/qemu-iotests/041
@@ -211,6 +211,11 @@
     test_small_buffer2 = None
     test_large_cluster = None
 
+class TestSingleDriveUnalignedLength(TestSingleDrive):
+    image_len = 1025 * 1024
+    test_small_buffer2 = None
+    test_large_cluster = None
+
 class TestMirrorNoBacking(ImageMirroringTestCase):
     image_len = 2 * 1024 * 1024 # MB
 
diff --git a/tests/qemu-iotests/041.out b/tests/qemu-iotests/041.out
index cfa5c0d..802ffaa 100644
--- a/tests/qemu-iotests/041.out
+++ b/tests/qemu-iotests/041.out
@@ -1,5 +1,5 @@
-...................................
+...........................................
 ----------------------------------------------------------------------
-Ran 35 tests
+Ran 43 tests
 
 OK