diff --git a/src/entity/gateway/inmemory.rs b/src/entity/gateway/inmemory.rs
index 560d683..ba6f665 100644
--- a/src/entity/gateway/inmemory.rs
+++ b/src/entity/gateway/inmemory.rs
@@ -21,8 +21,8 @@ where
     K: Ord + Copy,
     V: Clone,
 {
-    if !working_table.contains_key(&key) {
-        working_table.insert(key, original_table.get(&key)?.clone());
+    if let std::collections::btree_map::Entry::Vacant(e) = working_table.entry(key) {
+        e.insert(original_table.get(&key)?.clone());
     }
 
     Some(())