diff --git a/virtio-devices/src/block.rs b/virtio-devices/src/block.rs
index c7fc934c4..0f46ce389 100644
--- a/virtio-devices/src/block.rs
+++ b/virtio-devices/src/block.rs
@@ -773,7 +773,7 @@ impl Block {
     // TODO In future, we could add a `lock_granularity=` configuration to the CLI.
     // For now, we stick to QEMU behavior.
     fn lock_granularity(&mut self) -> LockGranularity {
-        self.disk_image.logical_size().map_or_else(
+        self.disk_image.physical_size().map_or_else(
             // use a safe fallback
             |e| {
                 let fallback = LockGranularity::WholeFile;