diff --git a/virtio-devices/src/block.rs b/virtio-devices/src/block.rs
index 5d7f89298..a580b40f2 100644
--- a/virtio-devices/src/block.rs
+++ b/virtio-devices/src/block.rs
@@ -616,7 +616,9 @@ impl Block {
                 (disk_nsectors, avail_features, 0, config, false)
             };
 
-        let serial = serial.map(Vec::from).unwrap_or(build_serial(&disk_path));
+        let serial = serial
+            .map(Vec::from)
+            .unwrap_or_else(|| build_serial(&disk_path));
 
         Ok(Block {
             common: VirtioCommon {
diff --git a/vm-allocator/src/system.rs b/vm-allocator/src/system.rs
index 96437f9a6..cb7770b2d 100644
--- a/vm-allocator/src/system.rs
+++ b/vm-allocator/src/system.rs
@@ -119,7 +119,7 @@ impl SystemAllocator {
         self.platform_mmio_address_space.allocate(
             address,
             size,
-            Some(align_size.unwrap_or(get_page_size())),
+            Some(align_size.unwrap_or_else(get_page_size)),
         )
     }
 
@@ -133,7 +133,7 @@ impl SystemAllocator {
         self.mmio_hole_address_space.allocate(
             address,
             size,
-            Some(align_size.unwrap_or(get_page_size())),
+            Some(align_size.unwrap_or_else(get_page_size)),
         )
     }