diff --git a/src/vm/obj/assemble.rs b/src/vm/obj/assemble.rs
index b59a352..9345eac 100644
--- a/src/vm/obj/assemble.rs
+++ b/src/vm/obj/assemble.rs
@@ -226,13 +226,16 @@ impl Assemble for Inst {
                 let mut bytes = Vec::with_capacity(len);
                 bytes.write_u16::<LE>($op).unwrap();
                 let source = $source;
-                let source_encoding = source.source_encoding();
+                let source_encoding = source.source_encoding() << 4;
                 bytes.write_u8(source_encoding).unwrap();
                 bytes.extend(source.assemble(asm)?);
                 assert_eq!(
-                    self.len(), bytes.len(),
+                    self.len(),
+                    bytes.len(),
                     "instruction size mismatch in {} instruction - {:?} produces these bytes {:?}",
-                    stringify!($op), self, bytes
+                    stringify!($op),
+                    self,
+                    bytes
                 );
                 Ok(bytes)
             }};