diff -ur wolfssl-3.13.0/src/ssl.c wolfssl-3.13.0-nginx/src/ssl.c
--- wolfssl-3.13.0/src/ssl.c	2017-12-21 10:23:04.000000000 +1000
+++ wolfssl-3.13.0-nginx/src/ssl.c	2018-04-17 09:46:47.364604657 +1000
@@ -20856,7 +20856,7 @@
 }
 #endif /* NO_RSA */
 
-#ifdef WOLFSSL_SIGNAL
+#if defined(WOLFSSL_SIGNAL) || defined(WOLFSSL_NGINX)
 int wolfSSL_HMAC_CTX_init(HMAC_CTX* ctx)
 {
     WOLFSSL_MSG("wolfSSL_HMAC_CTX_init");
diff -ur wolfssl-3.13.0/wolfssl/openssl/hmac.h wolfssl-3.13.0-nginx/wolfssl/openssl/hmac.h
--- wolfssl-3.13.0/wolfssl/openssl/hmac.h	2017-12-21 10:23:04.000000000 +1000
+++ wolfssl-3.13.0-nginx/wolfssl/openssl/hmac.h	2018-04-17 09:46:47.364604657 +1000
@@ -55,7 +55,7 @@
     int  type;
 } WOLFSSL_HMAC_CTX;
 
-#ifdef WOLFSSL_SIGNAL
+#if defined(WOLFSSL_SIGNAL) || defined(WOLFSSL_NGINX)
 WOLFSSL_API int wolfSSL_HMAC_CTX_init(WOLFSSL_HMAC_CTX* ctx);
 WOLFSSL_API int wolfSSL_HMAC_Init(WOLFSSL_HMAC_CTX* ctx, const void* key,
                                  int keylen, const EVP_MD* type);
diff -ur wolfssl-3.13.0/wolfssl/openssl/ssl.h wolfssl-3.13.0-nginx/wolfssl/openssl/ssl.h
--- wolfssl-3.13.0/wolfssl/openssl/ssl.h	2017-12-21 10:23:04.000000000 +1000
+++ wolfssl-3.13.0-nginx/wolfssl/openssl/ssl.h	2018-04-17 09:46:47.364604657 +1000
@@ -96,6 +96,8 @@
 #define CRYPTO_free   XFREE
 #define CRYPTO_malloc XMALLOC
 
+#define STACK_OF(x) WOLFSSL_STACK
+
 #define SSL_get_client_random(ssl,out,outSz) \
                                   wolfSSL_get_client_random((ssl),(out),(outSz))
 #define SSL_get_cipher_list(ctx,i)         wolfSSL_get_cipher_list_ex((ctx),(i))