diff --git a/deoxys/src/modes.rs b/deoxys/src/modes.rs
index dd56e030..2e5bc453 100644
--- a/deoxys/src/modes.rs
+++ b/deoxys/src/modes.rs
@@ -380,11 +380,13 @@ where
             });
         }
         let mut data = tail;
-        let index = blocks_len;
+        if !data.is_empty() {
+            let index = blocks_len;
 
-        encrypt_decrypt_block::<B, _>(index, tweak, subkeys, nonce, |block| {
-            data.xor_in2out((block[..data.len()]).into())
-        });
+            encrypt_decrypt_block::<B, _>(index, tweak, subkeys, nonce, |block| {
+                data.xor_in2out((block[..data.len()]).into())
+            });
+        }
     }
 }