diff --git a/src/stub/transaction.rs b/src/stub/transaction.rs
index 2e9ea2b..b697d54 100644
--- a/src/stub/transaction.rs
+++ b/src/stub/transaction.rs
@@ -13,7 +13,7 @@ impl Transaction {
         new_device_cb: F,
     ) -> Result<Self, crate::Error>
     where
-        F: Fn(String, &Fn() -> bool),
+        F: Fn(String, &dyn Fn() -> bool),
     {
         callback.call(Err(crate::Error::NotSupported));
         Err(crate::Error::NotSupported)