diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 853408438a..c57f39dd2b 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1182,7 +1182,7 @@ fail:
  * Return 0 on success and -errno in error cases
  */
 int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
-    int n_start, int n_end, int *num, uint64_t *host_offset, QCowL2Meta **m)
+    int *num, uint64_t *host_offset, QCowL2Meta **m)
 {
     BDRVQcowState *s = bs->opaque;
     uint64_t start, remaining;
@@ -1190,15 +1190,13 @@ int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
     uint64_t cur_bytes;
     int ret;
 
-    trace_qcow2_alloc_clusters_offset(qemu_coroutine_self(), offset,
-                                      n_start, n_end);
+    trace_qcow2_alloc_clusters_offset(qemu_coroutine_self(), offset, *num);
 
-    assert(n_start * BDRV_SECTOR_SIZE == offset_into_cluster(s, offset));
-    offset = start_of_cluster(s, offset);
+    assert((offset & ~BDRV_SECTOR_MASK) == 0);
 
 again:
-    start = offset + (n_start << BDRV_SECTOR_BITS);
-    remaining = (n_end - n_start) << BDRV_SECTOR_BITS;
+    start = offset;
+    remaining = *num << BDRV_SECTOR_BITS;
     cluster_offset = 0;
     *host_offset = 0;
     cur_bytes = 0;
@@ -1284,7 +1282,7 @@ again:
         }
     }
 
-    *num = (n_end - n_start) - (remaining >> BDRV_SECTOR_BITS);
+    *num -= remaining >> BDRV_SECTOR_BITS;
     assert(*num > 0);
     assert(*host_offset != 0);
 
diff --git a/block/qcow2.c b/block/qcow2.c
index 99a1ad13e6..a274d5f9f9 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1000,7 +1000,6 @@ static coroutine_fn int qcow2_co_writev(BlockDriverState *bs,
 {
     BDRVQcowState *s = bs->opaque;
     int index_in_cluster;
-    int n_end;
     int ret;
     int cur_nr_sectors; /* number of sectors in current iteration */
     uint64_t cluster_offset;
@@ -1024,14 +1023,16 @@ static coroutine_fn int qcow2_co_writev(BlockDriverState *bs,
 
         trace_qcow2_writev_start_part(qemu_coroutine_self());
         index_in_cluster = sector_num & (s->cluster_sectors - 1);
-        n_end = index_in_cluster + remaining_sectors;
+        cur_nr_sectors = remaining_sectors;
         if (s->crypt_method &&
-            n_end > QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors) {
-            n_end = QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors;
+            cur_nr_sectors >
+            QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors - index_in_cluster) {
+            cur_nr_sectors =
+                QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors - index_in_cluster;
         }
 
         ret = qcow2_alloc_cluster_offset(bs, sector_num << 9,
-            index_in_cluster, n_end, &cur_nr_sectors, &cluster_offset, &l2meta);
+            &cur_nr_sectors, &cluster_offset, &l2meta);
         if (ret < 0) {
             goto fail;
         }
@@ -1408,7 +1409,7 @@ static int preallocate(BlockDriverState *bs)
 
     while (nb_sectors) {
         num = MIN(nb_sectors, INT_MAX >> 9);
-        ret = qcow2_alloc_cluster_offset(bs, offset, 0, num, &num,
+        ret = qcow2_alloc_cluster_offset(bs, offset, &num,
                                          &host_offset, &meta);
         if (ret < 0) {
             return ret;
diff --git a/block/qcow2.h b/block/qcow2.h
index b5b7d13630..0b0eac899c 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -468,7 +468,7 @@ void qcow2_encrypt_sectors(BDRVQcowState *s, int64_t sector_num,
 int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
     int *num, uint64_t *cluster_offset);
 int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
-    int n_start, int n_end, int *num, uint64_t *host_offset, QCowL2Meta **m);
+    int *num, uint64_t *host_offset, QCowL2Meta **m);
 uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
                                          uint64_t offset,
                                          int compressed_size);
diff --git a/trace-events b/trace-events
index 1b668d1ac2..ab11f9721d 100644
--- a/trace-events
+++ b/trace-events
@@ -495,7 +495,7 @@ qcow2_writev_done_part(void *co, int cur_nr_sectors) "co %p cur_nr_sectors %d"
 qcow2_writev_data(void *co, uint64_t offset) "co %p offset %" PRIx64
 
 # block/qcow2-cluster.c
-qcow2_alloc_clusters_offset(void *co, uint64_t offset, int n_start, int n_end) "co %p offet %" PRIx64 " n_start %d n_end %d"
+qcow2_alloc_clusters_offset(void *co, uint64_t offset, int num) "co %p offet %" PRIx64 " num %d"
 qcow2_handle_copied(void *co, uint64_t guest_offset, uint64_t host_offset, uint64_t bytes) "co %p guest_offet %" PRIx64 " host_offset %" PRIx64 " bytes %" PRIx64
 qcow2_handle_alloc(void *co, uint64_t guest_offset, uint64_t host_offset, uint64_t bytes) "co %p guest_offet %" PRIx64 " host_offset %" PRIx64 " bytes %" PRIx64
 qcow2_do_alloc_clusters_offset(void *co, uint64_t guest_offset, uint64_t host_offset, int nb_clusters) "co %p guest_offet %" PRIx64 " host_offset %" PRIx64 " nb_clusters %d"