diff --git a/backend/src/pilstark/estark.rs b/backend/src/pilstark/estark.rs
index f423b9b74..b7b7b558d 100644
--- a/backend/src/pilstark/estark.rs
+++ b/backend/src/pilstark/estark.rs
@@ -113,7 +113,7 @@ impl<F: FieldElement> BackendImpl<F> for EStark {
             &setup.program,
             &pil,
             &self.params,
-            &"".to_string(),
+            "",
         )
         .unwrap();