diff --git a/backend/crates/infrastructure/src/cipher.rs b/backend/crates/infrastructure/src/cipher.rs
index 91ebde5..addc7f7 100644
--- a/backend/crates/infrastructure/src/cipher.rs
+++ b/backend/crates/infrastructure/src/cipher.rs
@@ -21,7 +21,7 @@ impl AesGcmCipher {
 }
 
 fn hex_decode(s: &str) -> anyhow::Result<Vec<u8>> {
-    anyhow::ensure!(s.len() % 2 == 0, "odd hex length");
+    anyhow::ensure!(s.len().is_multiple_of(2), "odd hex length");
     (0..s.len())
         .step_by(2)
         .map(|i| Ok(u8::from_str_radix(&s[i..i + 2], 16)?))