diff --git a/src/controller.rs b/src/controller.rs
index f378cbc6..ffc5dd5b 100644
--- a/src/controller.rs
+++ b/src/controller.rs
@@ -47,7 +47,7 @@ impl<'b> Controller<'b> {
&self,
inputs: Vec,
output_buffer: Option<&mut dyn std::fmt::Write>,
- handle_error: impl Fn(&Error, &mut dyn Write),
+ mut handle_error: impl FnMut(&Error, &mut dyn Write),
) -> Result {
let mut output_type;