diff --git a/block/qcow.c b/block/qcow.c
index 0c7b75bc76638944d4522f3705d37309ab07784b..6f9b2e2d2644d4b85587f2031092900330b76bfb 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -983,7 +983,7 @@ static int qcow_write_compressed(BlockDriverState *bs, int64_t sector_num,
         return ret;
     }
 
-    out_buf = g_malloc(s->cluster_size + (s->cluster_size / 1000) + 128);
+    out_buf = g_malloc(s->cluster_size);
 
     /* best compression, small window, no zlib header */
     memset(&strm, 0, sizeof(strm));
diff --git a/block/qcow2.c b/block/qcow2.c
index d620d0a85b514b4566dcdb70cd9879e4223f3dd3..91ef4dfefc75da7acb26974e61cb873226b9cf5b 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2612,7 +2612,7 @@ static int qcow2_write_compressed(BlockDriverState *bs, int64_t sector_num,
         return ret;
     }
 
-    out_buf = g_malloc(s->cluster_size + (s->cluster_size / 1000) + 128);
+    out_buf = g_malloc(s->cluster_size);
 
     /* best compression, small window, no zlib header */
     memset(&strm, 0, sizeof(strm));