diff --git a/primitives/io/src/lib.rs b/primitives/io/src/lib.rs
index 6eae364478e90..fd917f42f286f 100644
--- a/primitives/io/src/lib.rs
+++ b/primitives/io/src/lib.rs
@@ -1904,7 +1904,7 @@ mod tests {
 			}
 
 			// push invalid
-			let msg = format!("asdf!");
+			let msg = format!("asdf!".to_string());
 			let signature = pair.sign(msg.as_bytes());
 			crypto::sr25519_batch_verify(&signature, msg.as_bytes(), &pair_unused.public());
 			assert!(!crypto::finish_batch_verify());