diff --git a/librustzcash-wrapper/src/lib.rs b/librustzcash-wrapper/src/lib.rs
index ade568c..a09f3e6 100644
--- a/librustzcash-wrapper/src/lib.rs
+++ b/librustzcash-wrapper/src/lib.rs
@@ -728,6 +728,7 @@ pub extern "C" fn rust_wrapper_f4jumble(
     out: *mut u8,
     out_len: &mut usize) {
     let input: Vec<u8> = marshall_from_haskell_var(input, input_len, RW);
+    println!("testy mc testface");
     let result = f4jumble::f4jumble(&input).unwrap();
     marshall_to_haskell_var(&result, out, out_len, RW);
 }