diff --git a/src/Utils.cpp b/src/Utils.cpp
index 186c8720a..a07de2e8d 100644
--- a/src/Utils.cpp
+++ b/src/Utils.cpp
@@ -81,7 +81,10 @@ int Utils::MACThenDecrypt(const uint8_t* shared_secret, uint8_t* dest, const uin
     sha.update(src + CIPHER_MAC_SIZE, src_len - CIPHER_MAC_SIZE);
     sha.finalizeHMAC(shared_secret, PUB_KEY_SIZE, hmac, CIPHER_MAC_SIZE);
   }
-  if (memcmp(hmac, src, CIPHER_MAC_SIZE) == 0) {
+  // constant-time comparison to prevent timing side-channel attacks
+  uint8_t diff = 0;
+  for (int i = 0; i < CIPHER_MAC_SIZE; i++) diff |= hmac[i] ^ src[i];
+  if (diff == 0) {
     return decrypt(shared_secret, dest, src + CIPHER_MAC_SIZE, src_len - CIPHER_MAC_SIZE);
   }
   return 0; // invalid HMAC