From OpenBSD.

diff --git a/src/client.c b/src/client.c
index 6a5aeb3..d416127 100644
--- a/src/client.c
+++ b/src/client.c
@@ -753,7 +753,7 @@ NOEXPORT void print_cipher(CLI *c) { /* print negotiated cipher */
 NOEXPORT void transfer(CLI *c) {
     int timeout; /* s_poll_wait timeout in seconds */
     int pending; /* either processed on unprocessed TLS data */
-#if OPENSSL_VERSION_NUMBER >= 0x10100000L
+#if OPENSSL_VERSION_NUMBER >= 0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
     int has_pending=0, prev_has_pending;
 #endif
     int watchdog=0; /* a counter to detect an infinite loop */
@@ -800,7 +800,7 @@ NOEXPORT void transfer(CLI *c) {
 
         /****************************** wait for an event */
         pending=SSL_pending(c->ssl);
-#if OPENSSL_VERSION_NUMBER >= 0x10100000L
+#if OPENSSL_VERSION_NUMBER >= 0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
         /* only attempt to process SSL_has_pending() data once */
         prev_has_pending=has_pending;
         has_pending=SSL_has_pending(c->ssl);
@@ -1205,7 +1205,7 @@ NOEXPORT void transfer(CLI *c) {
             s_log(LOG_ERR,
                 "please report the problem to Michal.Trojnara@stunnel.org");
             stunnel_info(LOG_ERR);
-#if OPENSSL_VERSION_NUMBER >= 0x10100000L
+#if OPENSSL_VERSION_NUMBER >= 0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
             s_log(LOG_ERR, "protocol=%s, SSL_pending=%d, SSL_has_pending=%d",
                 SSL_get_version(c->ssl),
                 SSL_pending(c->ssl), SSL_has_pending(c->ssl));
diff --git a/src/common.h b/src/common.h
index bc37eb5..87bfe54 100644
--- a/src/common.h
+++ b/src/common.h
@@ -457,7 +457,7 @@ extern char *sys_errlist[];
 #define OPENSSL_NO_TLS1_2
 #endif /* OpenSSL older than 1.0.1 || defined(OPENSSL_NO_TLS1) */
 
-#if OPENSSL_VERSION_NUMBER>=0x10100000L
+#if OPENSSL_VERSION_NUMBER>=0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
 #ifndef OPENSSL_NO_SSL2
 #define OPENSSL_NO_SSL2
 #endif /* !defined(OPENSSL_NO_SSL2) */
diff --git a/src/ctx.c b/src/ctx.c
index a2202b7..a39ee4c 100644
--- a/src/ctx.c
+++ b/src/ctx.c
@@ -94,7 +94,7 @@ NOEXPORT void set_prompt(const char *);
 NOEXPORT int ui_retry(void);
 
 /* session tickets */
-#if OPENSSL_VERSION_NUMBER >= 0x10101000L
+#if OPENSSL_VERSION_NUMBER >= 0x10101000L && !defined(LIBRESSL_VERSION_NUMBER)
 NOEXPORT int generate_session_ticket_cb(SSL *, void *);
 NOEXPORT int decrypt_session_ticket_cb(SSL *, SSL_SESSION *,
     const unsigned char *, size_t, SSL_TICKET_STATUS, void *);
@@ -182,7 +182,7 @@ int context_init(SERVICE_OPTIONS *section) { /* init TLS context */
     }
     current_section=section; /* setup current section for callbacks */
 
-#if OPENSSL_VERSION_NUMBER>=0x10100000L
+#if OPENSSL_VERSION_NUMBER>=0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
     /* set the security level */
     if(section->security_level>=0) {
         /* set the user-specified value */
@@ -270,7 +270,7 @@ int context_init(SERVICE_OPTIONS *section) { /* init TLS context */
 #endif
 
     /* setup session tickets */
-#if OPENSSL_VERSION_NUMBER >= 0x10101000L
+#if OPENSSL_VERSION_NUMBER >= 0x10101000L && !defined(LIBRESSL_VERSION_NUMBER)
     SSL_CTX_set_session_ticket_cb(section->ctx, generate_session_ticket_cb,
         decrypt_session_ticket_cb, NULL);
 #endif /* OpenSSL 1.1.1 or later */
@@ -544,7 +544,7 @@ NOEXPORT int ecdh_init(SERVICE_OPTIONS *section) {
 /**************************************** initialize OpenSSL CONF */
 
 NOEXPORT int conf_init(SERVICE_OPTIONS *section) {
-#if OPENSSL_VERSION_NUMBER>=0x10002000L
+#if OPENSSL_VERSION_NUMBER>=0x10002000L && !defined(LIBRESSL_VERSION_NUMBER)
     SSL_CONF_CTX *cctx;
     NAME_LIST *curr;
     char *cmd, *param;
@@ -1050,7 +1050,7 @@ NOEXPORT int ui_retry() {
 
 /**************************************** session tickets */
 
-#if OPENSSL_VERSION_NUMBER >= 0x10101000L
+#if OPENSSL_VERSION_NUMBER >= 0x10101000L && !defined(LIBRESSL_VERSION_NUMBER)
 
 typedef struct {
     void *session_authenticated;
@@ -1541,7 +1541,7 @@ NOEXPORT void info_callback(const SSL *ssl, int where, int ret) {
 
     c=SSL_get_ex_data(ssl, index_ssl_cli);
     if(c) {
-#if OPENSSL_VERSION_NUMBER>=0x10100000L
+#if OPENSSL_VERSION_NUMBER>=0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
         OSSL_HANDSHAKE_STATE state=SSL_get_state(ssl);
 #else
         int state=SSL_get_state((SSL *)ssl);
@@ -1575,7 +1575,10 @@ NOEXPORT void info_callback(const SSL *ssl, int where, int ret) {
             if(state==TLS_ST_SR_CLNT_HELLO) {
 #else
             if(state==SSL3_ST_SR_CLNT_HELLO_A
-                    || state==SSL23_ST_SR_CLNT_HELLO_A) {
+#if !defined(LIBRESSL_VERSION_NUMBER) || LIBRESSL_VERSION_NUMBER < 0x4000000fL
+                    || state==SSL23_ST_SR_CLNT_HELLO_A
+#endif
+            ) {
 #endif
                 /* client hello received after initial handshake,
                  * this means renegotiation -> mark it */
diff --git a/src/options.c b/src/options.c
index 9ac9c7e..dfcf8b2 100644
--- a/src/options.c
+++ b/src/options.c
@@ -37,7 +37,7 @@
 
 #include "prototypes.h"
 
-#if OPENSSL_VERSION_NUMBER >= 0x10101000L
+#if OPENSSL_VERSION_NUMBER >= 0x10101000L && !defined(LIBRESSL_VERSION_NUMBER)
 #define DEFAULT_CURVES "X25519:P-256:X448:P-521:P-384"
 #else /* OpenSSL version < 1.1.1 */
 #define DEFAULT_CURVES "prime256v1"
diff --git a/src/prototypes.h b/src/prototypes.h
index 89d77b8..832942d 100644
--- a/src/prototypes.h
+++ b/src/prototypes.h
@@ -726,7 +726,7 @@ int getnameinfo(const struct sockaddr *, socklen_t,
 extern CLI *thread_head;
 #endif
 
-#if OPENSSL_VERSION_NUMBER<0x10100004L
+#if OPENSSL_VERSION_NUMBER<0x10100004L || defined(LIBRESSL_VERSION_NUMBER)
 
 #ifdef USE_OS_THREADS
 
@@ -777,7 +777,7 @@ typedef enum {
 
 extern CRYPTO_RWLOCK *stunnel_locks[STUNNEL_LOCKS];
 
-#if OPENSSL_VERSION_NUMBER<0x10100004L
+#if OPENSSL_VERSION_NUMBER<0x10100004L || defined(LIBRESSL_VERSION_NUMBER)
 /* Emulate the OpenSSL 1.1 locking API for older OpenSSL versions */
 CRYPTO_RWLOCK *CRYPTO_THREAD_lock_new(void);
 int CRYPTO_THREAD_read_lock(CRYPTO_RWLOCK *);
diff --git a/src/ssl.c b/src/ssl.c
index fd6106b..526da34 100644
--- a/src/ssl.c
+++ b/src/ssl.c
@@ -43,7 +43,7 @@ NOEXPORT void cb_new_auth(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
 #if OPENSSL_VERSION_NUMBER>=0x30000000L
 NOEXPORT int cb_dup_addr(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from,
     void **from_d, int idx, long argl, void *argp);
-#elif OPENSSL_VERSION_NUMBER>=0x10100000L
+#elif OPENSSL_VERSION_NUMBER>=0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
 NOEXPORT int cb_dup_addr(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from,
     void *from_d, int idx, long argl, void *argp);
 #else
@@ -102,7 +102,7 @@ int fips_available() { /* either FIPS provider or container is available */
 
 /* initialize libcrypto before invoking API functions that require it */
 void crypto_init(char *stunnel_dir) {
-#if OPENSSL_VERSION_NUMBER>=0x10100000L
+#if OPENSSL_VERSION_NUMBER>=0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
     OPENSSL_INIT_SETTINGS *conf=OPENSSL_INIT_new();
 #ifdef USE_WIN32
     char *path;
@@ -200,7 +200,7 @@ NOEXPORT void cb_new_auth(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
 #if OPENSSL_VERSION_NUMBER>=0x30000000L
 NOEXPORT int cb_dup_addr(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from,
         void **from_d, int idx, long argl, void *argp) {
-#elif OPENSSL_VERSION_NUMBER>=0x10100000L
+#elif OPENSSL_VERSION_NUMBER>=0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
 NOEXPORT int cb_dup_addr(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from,
         void *from_d, int idx, long argl, void *argp) {
 #else
diff --git a/src/sthreads.c b/src/sthreads.c
index e3e442e..9f343e9 100644
--- a/src/sthreads.c
+++ b/src/sthreads.c
@@ -123,7 +123,7 @@ NOEXPORT void thread_id_init() {
 /**************************************** locking */
 
 /* we only need to initialize locking with OpenSSL older than 1.1.0 */
-#if OPENSSL_VERSION_NUMBER<0x10100004L
+#if OPENSSL_VERSION_NUMBER<0x10100004L || defined(LIBRESSL_VERSION_NUMBER)
 
 #ifdef USE_PTHREAD
 
@@ -283,7 +283,7 @@ NOEXPORT int s_atomic_add(int *val, int amount, CRYPTO_RWLOCK *lock) {
 
 CRYPTO_RWLOCK *stunnel_locks[STUNNEL_LOCKS];
 
-#if OPENSSL_VERSION_NUMBER<0x10100004L
+#if OPENSSL_VERSION_NUMBER<0x10100004L || defined(LIBRESSL_VERSION_NUMBER)
 
 #ifdef USE_OS_THREADS
 
@@ -391,7 +391,8 @@ int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock) {
 
 NOEXPORT void locking_init() {
     size_t i;
-#if defined(USE_OS_THREADS) && OPENSSL_VERSION_NUMBER<0x10100004L
+#if defined(USE_OS_THREADS) && \
+	(OPENSSL_VERSION_NUMBER<0x10100004L || defined(LIBRESSL_VERSION_NUMBER))
     size_t num;
 
     /* initialize the OpenSSL static locking */
diff --git a/src/tls.c b/src/tls.c
index 43266d3..5de3435 100644
--- a/src/tls.c
+++ b/src/tls.c
@@ -40,7 +40,7 @@
 volatile int tls_initialized=0;
 
 NOEXPORT void tls_platform_init(void);
-#if OPENSSL_VERSION_NUMBER<0x10100000L
+#if OPENSSL_VERSION_NUMBER<0x10100000L || defined(LIBRESSL_VERSION_NUMBER)
 NOEXPORT void free_function(void *);
 #endif
 
@@ -51,7 +51,7 @@ void tls_init() {
     tls_platform_init();
     tls_initialized=1;
     ui_tls=tls_alloc(NULL, NULL, "ui");
-#if OPENSSL_VERSION_NUMBER>=0x10100000L
+#if OPENSSL_VERSION_NUMBER>=0x10100000L && !defined(LIBRESSL_VERSION_NUMBER)
     CRYPTO_set_mem_functions(str_alloc_detached_debug,
         str_realloc_detached_debug, str_free_debug);
 #else
@@ -183,7 +183,7 @@ TLS_DATA *tls_get() {
 
 /**************************************** OpenSSL allocator hook */
 
-#if OPENSSL_VERSION_NUMBER<0x10100000L
+#if OPENSSL_VERSION_NUMBER<0x10100000L || defined(LIBRESSL_VERSION_NUMBER)
 NOEXPORT void free_function(void *ptr) {
     /* CRYPTO_set_mem_ex_functions() needs a function rather than a macro */
     /* unfortunately, OpenSSL provides no file:line information here */
diff --git a/src/verify.c b/src/verify.c
index 4058d6c..dbb4880 100644
--- a/src/verify.c
+++ b/src/verify.c
@@ -350,7 +350,7 @@ NOEXPORT int cert_check_local(X509_STORE_CTX *callback_ctx) {
     cert=X509_STORE_CTX_get_current_cert(callback_ctx);
     subject=X509_get_subject_name(cert);
 
-#if OPENSSL_VERSION_NUMBER<0x10100006L
+#if OPENSSL_VERSION_NUMBER<0x10100006L || defined(LIBRESSL_VERSION_NUMBER)
 #define X509_STORE_CTX_get1_certs X509_STORE_get1_certs
 #endif
     /* modern API allows retrieving multiple matching certificates */