diff --git a/02-peer-protocol.md b/02-peer-protocol.md
index 0518ff6..b9faa7c 100644
--- a/02-peer-protocol.md
+++ b/02-peer-protocol.md
@@ -416,6 +416,9 @@ The receiving node:
   - SHOULD apply the `witnesses` to the transaction and broadcast it
   - MUST reply with their `tx_signatures` if not already transmitted
 
+Both nodes:
+  - MUST sign the transaction using SIGHASH_ALL
+
 #### Rationale
 
 A strict ordering is used to decide which peer sends `tx_signatures` first.