https://bugs.gentoo.org/696220
--- a/cryptonite.cabal
+++ b/cryptonite.cabal
@@ -276,6 +276,7 @@ Library
                    , cbits/cryptonite_aes.c
 
   if arch(x86_64) || flag(support_blake2_sse)
+    CC-options:     -msse2
     C-sources:      cbits/blake2/sse/blake2s.c
                   , cbits/blake2/sse/blake2sp.c
                   , cbits/blake2/sse/blake2b.c