diff --git a/node/AES-aesni.c b/node/AES-aesni.c
index 2d808b97b..a5fc81e6d 100644
--- a/node/AES-aesni.c
+++ b/node/AES-aesni.c
@@ -11,6 +11,11 @@
  */
 /****/
 
+/* This is done in plain C because the compiler (at least GCC and CLANG) seem
+ * to do a *slightly* better job optimizing this intrinsic code when compiling
+ * plain C. C also gives us the register hint keyword, which seems to actually
+ * make a small difference. */
+
 #if (defined(__amd64) || defined(__amd64__) || defined(__x86_64) || defined(__x86_64__) || defined(__AMD64) || defined(__AMD64__) || defined(_M_X64))
 
 #include <stdint.h>