diff --git a/src/MQTTClient.c b/src/MQTTClient.c
index 57ecf3242b4e60adf26fcd04233b27caab197175..a5fab47588d1b1773f99972d5de4f7e624a119a4 100644
--- a/src/MQTTClient.c
+++ b/src/MQTTClient.c
@@ -250,7 +250,7 @@ static pthread_mutex_t mqttclient_mutex_store = PTHREAD_MUTEX_INITIALIZER;
 static mutex_type mqttclient_mutex = &mqttclient_mutex_store;
 
 static pthread_mutex_t socket_mutex_store = PTHREAD_MUTEX_INITIALIZER;
-static mutex_type socket_mutex = &socket_mutex_store;
+mutex_type socket_mutex = &socket_mutex_store;
 
 static pthread_mutex_t subscribe_mutex_store = PTHREAD_MUTEX_INITIALIZER;
 static mutex_type subscribe_mutex = &subscribe_mutex_store;
diff --git a/src/Socket.c b/src/Socket.c
index 57cdf99c29024f76f9f8a552fd08e5fa2c7d12e0..9a91c58d9dc42ccbeea886fb64d50408510b6a9d 100644
--- a/src/Socket.c
+++ b/src/Socket.c
@@ -74,6 +74,8 @@ Sockets mod_s;
 static fd_set wset;
 #endif
 
+extern mutex_type socket_mutex;
+
 /**
  * Set a socket non-blocking, OS independently
  * @param sock the socket to set non-blocking
@@ -268,6 +270,7 @@ int Socket_addSocket(SOCKET newSd)
 	int rc = 0;
 
 	FUNC_ENTRY;
+	Thread_lock_mutex(socket_mutex);
 	mod_s.nfds++;
 	if (mod_s.fds_read)
 		mod_s.fds_read = realloc(mod_s.fds_read, mod_s.nfds * sizeof(mod_s.fds_read[0]));
@@ -307,6 +310,7 @@ int Socket_addSocket(SOCKET newSd)
 		Log(LOG_ERROR, -1, "addSocket: setnonblocking");
 
 exit:
+	Thread_unlock_mutex(socket_mutex);
 	FUNC_EXIT_RC(rc);
 	return rc;
 }
@@ -1169,6 +1173,7 @@ int Socket_new(const char* addr, size_t addr_len, int port, SOCKET* sock)
 				if (rc == EINPROGRESS || rc == EWOULDBLOCK)
 				{
 					SOCKET* pnewSd = (SOCKET*)malloc(sizeof(SOCKET));
+					ListElement* result = NULL;
 
 					if (!pnewSd)
 					{
@@ -1176,7 +1181,10 @@ int Socket_new(const char* addr, size_t addr_len, int port, SOCKET* sock)
 						goto exit;
 					}
 					*pnewSd = *sock;
-					if (!ListAppend(mod_s.connect_pending, pnewSd, sizeof(SOCKET)))
+					Thread_lock_mutex(socket_mutex);
+					result = ListAppend(mod_s.connect_pending, pnewSd, sizeof(SOCKET));
+					Thread_unlock_mutex(socket_mutex);
+					if (!result)
 					{
 						free(pnewSd);
 						rc = PAHO_MEMORY_ERROR;
@@ -1189,7 +1197,9 @@ int Socket_new(const char* addr, size_t addr_len, int port, SOCKET* sock)
                as reported in https://github.com/eclipse/paho.mqtt.c/issues/135 */
             if (rc != 0 && (rc != EINPROGRESS) && (rc != EWOULDBLOCK))
             {
+				Thread_lock_mutex(socket_mutex);
             	Socket_close(*sock); /* close socket and remove from our list of sockets */
+				Thread_unlock_mutex(socket_mutex);
                 *sock = SOCKET_ERROR; /* as initialized before */
             }
 		}