diff --git a/lightning/src/crypto/chacha20.rs b/lightning/src/crypto/chacha20.rs
index 5b0c16c933f..67f9e93c480 100644
--- a/lightning/src/crypto/chacha20.rs
+++ b/lightning/src/crypto/chacha20.rs
@@ -321,6 +321,7 @@ mod fuzzy_chacha {
 		) {
 			debug_assert_eq!(dest.len(), src.len());
 			debug_assert!(dest.len() <= 32);
+			dest.copy_from_slice(src);
 		}
 
 		pub fn encrypt_single_block_in_place(