diff --git a/bscrypt.cpp b/bscrypt.cpp
index 3e8f201..957484f 100644
--- a/bscrypt.cpp
+++ b/bscrypt.cpp
@@ -562,12 +562,13 @@ int bscrypt_kdf(void *output, size_t outputSize, const void *password, size_t pa
 
 	// Step 3: output = kdf(work, seed)
 	uint64_t i = 1;
+	uint64_t workSeed0 = workSeed[0];
 	while (outputSize > 64)
 	{
 		blake2b_nativeIn(output, 64, workSeed, 16 * sizeof(uint64_t));
 		output = ((uint8_t*) output) + 64;
 		outputSize -= 64;
-		workSeed[0] ^= i;
+		workSeed[0] = workSeed0 ^ i;
 		i++;
 	}
 	if (outputSize != 0)