diff --git a/src/lib.rs b/src/lib.rs
index c50e64c..d218a83 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -25,8 +25,12 @@ pub struct Obligation {
 }
 
 impl Obligation {
-    fn serialize(self) -> Vec<u8> {
-        [&self.from[..], &self.value.to_le_bytes()[..], &self.to[..]].concat()
+    fn serialize(self) -> [u8; 68] {
+        let mut arr = [0; 68];
+        arr[..32].clone_from_slice(&self.from);
+        arr[32..36].clone_from_slice(&self.value.to_le_bytes());
+        arr[36..].clone_from_slice(&self.to);
+        arr
     }
 }