diff --git a/crates/crypto/src/chacha20_poly1305.rs b/crates/crypto/src/chacha20_poly1305.rs
index 28ed6af..acef060 100644
--- a/crates/crypto/src/chacha20_poly1305.rs
+++ b/crates/crypto/src/chacha20_poly1305.rs
@@ -264,11 +264,13 @@ fn poly1305_mac(key: &[u8; 32], data: &[u8]) -> [u8; 16] {
     g1 &= mask;
     g2 &= mask;
     g3 &= mask;
+    let g4 = g4 & mask;
     let nmask = !mask;
     h0 = (h0 & nmask) | g0;
     h1 = (h1 & nmask) | g1;
     h2 = (h2 & nmask) | g2;
     h3 = (h3 & nmask) | g3;
+    h4 = (h4 & nmask) | g4;
 
     // Reassemble h as a 128-bit number (mod 2^128) and add s
     let h_val: u128 = (h0 as u128)