diff --git a/book/src/zkas/bincode.md b/book/src/zkas/bincode.md
index 5e0b312f9..e4c89c89e 100644
--- a/book/src/zkas/bincode.md
+++ b/book/src/zkas/bincode.md
@@ -35,6 +35,10 @@ OPCODE ARG_NUM STACK_INDEX ... STACK_INDEX
 TBD
 ```
 
+Integers in the binary are encoded using variable-integer encoding.
+See [`serial.rs`](../../../src/util/serial.rs) for our Rust
+implementation.
+
 ## `MAGIC_BYTES`
 
 The magic bytes are the file signature consisting of four bytes used