diff --git a/src/pcnt.rs b/src/pcnt.rs
index 086748c9040..b23e251fba4 100644
--- a/src/pcnt.rs
+++ b/src/pcnt.rs
@@ -526,7 +526,7 @@ impl<'d> PcntDriver<'d> {
         unsafe {
             ISR_HANDLERS[self.unit as usize] = Some(core::mem::transmute::<
                 alloc::boxed::Box<dyn FnMut(u32)>,
-                IsrHandler,
+                alloc::boxed::Box<dyn FnMut(u32)>,
             >(callback));
         }
         esp!(unsafe {