diff --git a/src/lib.rs b/src/lib.rs
index 580be2c..1bd593c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -51,6 +51,7 @@ mod tictoc {
             Ok(Init::new())
         }
     
+        #[pyo3(signature = (tic=None))]
         fn toc(&mut self, tic: Option<Init>) -> PyResult<Results> {
             let elapsed_time = match tic {
                 Some(ref tic) => tic.time.elapsed(),