diff --git a/chacha_avx.cpp b/chacha_avx.cpp
index f9565304..67a8affa 100644
--- a/chacha_avx.cpp
+++ b/chacha_avx.cpp
@@ -374,7 +374,7 @@ void ChaCha_OperateKeystream_AVX2(const word32 *state, const byte* input, byte *
         _mm256_storeu_si256(output_mm + 15, _mm256_permute2x128_si256(X3_2, X3_3, 0 + (2 << 4)));
     }
 
-    // https://stackoverflow.com/a/7841251/608639
+    // https://software.intel.com/en-us/articles/avoiding-avx-sse-transition-penalties
     _mm256_zeroupper();
 }