diff --git a/virtio-devices/src/iommu.rs b/virtio-devices/src/iommu.rs
index 5afc30b8f..815f22d5f 100644
--- a/virtio-devices/src/iommu.rs
+++ b/virtio-devices/src/iommu.rs
@@ -436,9 +436,7 @@ impl Request {
 
                 // Add new domain with no mapping if the entry didn't exist yet
                 let mut mappings = mapping.mappings.write().unwrap();
-                if !mappings.contains_key(&domain) {
-                    mappings.insert(domain, BTreeMap::new());
-                }
+                mappings.entry(domain).or_insert_with(BTreeMap::new);
 
                 0
             }