diff --git a/qemu-img.c b/qemu-img.c
index ace3adf..9fe94df 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -4371,7 +4371,7 @@
     struct timeval t1, t2;
     int i;
     bool force_share = false;
-    size_t buf_size;
+    size_t buf_size = 0;
 
     for (;;) {
         static const struct option long_options[] = {
@@ -4593,7 +4593,7 @@
 
 out:
     if (data.buf) {
-        blk_unregister_buf(blk, data.buf);
+        blk_unregister_buf(blk, data.buf, buf_size);
     }
     qemu_vfree(data.buf);
     blk_unref(blk);