Index: src/sthreads.c
--- src/sthreads.c.orig
+++ src/sthreads.c
@@ -120,7 +120,7 @@ void thread_id_init(void) {
 /**************************************** 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
 
@@ -279,7 +279,7 @@ NOEXPORT int s_atomic_add(int *val, int amount, CRYPTO
 
 CRYPTO_RWLOCK *stunnel_locks[STUNNEL_LOCKS];
 
-#if OPENSSL_VERSION_NUMBER<0x10100004L
+#if OPENSSL_VERSION_NUMBER<0x10100004L || defined(LIBRESSL_VERSION_NUMBER)
 
 #ifdef USE_OS_THREADS
 
@@ -387,7 +387,8 @@ int CRYPTO_atomic_add(int *val, int amount, int *ret, 
 
 void locking_init(void) {
     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 */