diff --git a/masque/utils/deferreddict.py b/masque/utils/deferreddict.py
index 02c1a22..31e6943 100644
--- a/masque/utils/deferreddict.py
+++ b/masque/utils/deferreddict.py
@@ -60,4 +60,4 @@ class DeferredDict(dict, Generic[Key, Value]):
         Convenience function to avoid having to manually wrap
          constant values into callables.
         """
-        self[key] = lambda: value
+        self[key] = lambda v=value: v