diff --git a/crypto/cipher_extra/e_aesgcmsiv.c b/crypto/cipher_extra/e_aesgcmsiv.c
index e3534bb..71a71fa 100644
--- a/crypto/cipher_extra/e_aesgcmsiv.c
+++ b/crypto/cipher_extra/e_aesgcmsiv.c
@@ -27,7 +27,11 @@
 #define EVP_AEAD_AES_GCM_SIV_NONCE_LEN 12
 #define EVP_AEAD_AES_GCM_SIV_TAG_LEN 16
 
-#if defined(OPENSSL_X86_64) && !defined(OPENSSL_NO_ASM)
+// TODO(davidben): AES-GCM-SIV assembly is not correct for Windows. It must save
+// and restore xmm6 through xmm15.
+#if defined(OPENSSL_X86_64) && !defined(OPENSSL_NO_ASM) && \
+    !defined(OPENSSL_WINDOWS)
+#define AES_GCM_SIV_ASM
 
 // Optimised AES-GCM-SIV
 
@@ -549,7 +553,7 @@
     NULL /* tag_len */,
 };
 
-#endif  // X86_64 && !NO_ASM
+#endif  // X86_64 && !NO_ASM && !WINDOWS
 
 struct aead_aes_gcm_siv_ctx {
   union {
@@ -838,7 +842,7 @@
     NULL /* tag_len */,
 };
 
-#if defined(OPENSSL_X86_64) && !defined(OPENSSL_NO_ASM)
+#if defined(AES_GCM_SIV_ASM)
 
 static char avx_aesni_capable(void) {
   const uint32_t ecx = OPENSSL_ia32cap_P[1];
@@ -871,4 +875,4 @@
   return &aead_aes_256_gcm_siv;
 }
 
-#endif  // X86_64 && !NO_ASM
+#endif  // AES_GCM_SIV_ASM