diff --git a/block/qcow2.c b/block/qcow2.c
index a1773e4790f35e761aa895cff3ba4905a920d15b..28338bf9d0d215c48bb45f8210753f5ccbb2fcdf 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -355,7 +355,7 @@ int qcow2_backing_read1(BlockDriverState *bs, QEMUIOVector *qiov,
     else
         n1 = bs->total_sectors - sector_num;
 
-    qemu_iovec_memset(qiov, 0, 512 * (nb_sectors - n1));
+    qemu_iovec_memset_skip(qiov, 0, 512 * (nb_sectors - n1), 512 * n1);
 
     return n1;
 }
@@ -478,8 +478,7 @@ static void qcow2_aio_read_cb(void *opaque, int ret)
             if (n1 > 0) {
                 BLKDBG_EVENT(bs->file, BLKDBG_READ_BACKING_AIO);
                 acb->hd_aiocb = bdrv_aio_readv(bs->backing_hd, acb->sector_num,
-                                    &acb->hd_qiov, acb->cur_nr_sectors,
-				    qcow2_aio_read_cb, acb);
+                                    &acb->hd_qiov, n1, qcow2_aio_read_cb, acb);
                 if (acb->hd_aiocb == NULL)
                     goto done;
             } else {
diff --git a/cutils.c b/cutils.c
index 8d562b28ab0d5fb71c0fa88a44cdcdcd623af2b2..f9a7e3689e04605beebabef940f280e1a8fca572 100644
--- a/cutils.c
+++ b/cutils.c
@@ -267,6 +267,37 @@ void qemu_iovec_memset(QEMUIOVector *qiov, int c, size_t count)
     }
 }
 
+void qemu_iovec_memset_skip(QEMUIOVector *qiov, int c, size_t count,
+                            size_t skip)
+{
+    int i;
+    size_t done;
+    void *iov_base;
+    uint64_t iov_len;
+
+    done = 0;
+    for (i = 0; (i < qiov->niov) && (done != count); i++) {
+        if (skip >= qiov->iov[i].iov_len) {
+            /* Skip the whole iov */
+            skip -= qiov->iov[i].iov_len;
+            continue;
+        } else {
+            /* Skip only part (or nothing) of the iov */
+            iov_base = (uint8_t*) qiov->iov[i].iov_base + skip;
+            iov_len = qiov->iov[i].iov_len - skip;
+            skip = 0;
+        }
+
+        if (done + iov_len > count) {
+            memset(iov_base, c, count - done);
+            break;
+        } else {
+            memset(iov_base, c, iov_len);
+        }
+        done += iov_len;
+    }
+}
+
 #ifndef _WIN32
 /* Sets a specific flag */
 int fcntl_setfl(int fd, int flag)
diff --git a/qemu-common.h b/qemu-common.h
index c7ff280b952f41f06c033ba1085f789406a3cc98..cb4b7e0d386f596c0b81fc44505621336f907e8e 100644
--- a/qemu-common.h
+++ b/qemu-common.h
@@ -322,6 +322,8 @@ void qemu_iovec_reset(QEMUIOVector *qiov);
 void qemu_iovec_to_buffer(QEMUIOVector *qiov, void *buf);
 void qemu_iovec_from_buffer(QEMUIOVector *qiov, const void *buf, size_t count);
 void qemu_iovec_memset(QEMUIOVector *qiov, int c, size_t count);
+void qemu_iovec_memset_skip(QEMUIOVector *qiov, int c, size_t count,
+                            size_t skip);
 
 struct Monitor;
 typedef struct Monitor Monitor;