diff --git a/lindi/LindiH5pyFile/LindiReferenceFileSystemStore.py b/lindi/LindiH5pyFile/LindiReferenceFileSystemStore.py
index 48b2801..b6c380a 100644
--- a/lindi/LindiH5pyFile/LindiReferenceFileSystemStore.py
+++ b/lindi/LindiH5pyFile/LindiReferenceFileSystemStore.py
@@ -115,6 +115,9 @@ def __init__(self, rfs: dict, *, mode: Literal["r", "r+"] = "r+", local_cache: U
         self.local_cache = local_cache
 
     # These methods are overridden from MutableMapping
+    def __contains__(self, key: str):
+        return key in self.rfs["refs"]
+
     def __getitem__(self, key: str):
         if key not in self.rfs["refs"]:
             raise KeyError(key)