diff --git a/configure.in b/configure.in
index 47567af..f217231 100644
--- a/configure.in
+++ b/configure.in
@@ -46,6 +46,7 @@ AC_ARG_ENABLE([cli],
 AM_CONDITIONAL([ENABLE_CLI], [test "$enable_cli" = "yes"])
 
 AC_CHECK_LIB([m], [pow], [], AC_MSG_ERROR([libm is required]))
+AC_CHECK_LIB([pthread], [pthread_mutex_lock], [], AC_MSG_ERROR([libpthread is required]))
 
 AC_CONFIG_FILES([Makefile doc/Doxyfile doc/Makefile lib/Makefile
 	include/Makefile src/Makefile src/lib/Makefile man/Makefile
diff --git a/lib/socket.c b/lib/socket.c
index ebdf4e8..461cd41 100644
--- a/lib/socket.c
+++ b/lib/socket.c
@@ -15,6 +15,8 @@
  * @{
  */
 
+#include <pthread.h>
+
 #include <netlink-local.h>
 #include <netlink/netlink.h>
 #include <netlink/utils.h>
@@ -43,12 +45,15 @@ static void __init init_default_cb(void)
 }
 
 static uint32_t used_ports_map[32];
+static pthread_mutex_t port_map_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 static uint32_t generate_local_port(void)
 {
 	int i, n;
 	uint32_t pid = getpid() & 0x3FFFFF;
 
+	pthread_mutex_lock(&port_map_mutex);
+
 	for (i = 0; i < 32; i++) {
 		if (used_ports_map[i] == 0xFFFFFFFF)
 			continue;
@@ -62,11 +67,15 @@ static uint32_t generate_local_port(void)
 
 			/* PID_MAX_LIMIT is currently at 2^22, leaving 10 bit
 			 * to, i.e. 1024 unique ports per application. */
-			return pid + (n << 22);
 
+			pthread_mutex_unlock(&port_map_mutex);
+
+			return pid + (n << 22);
 		}
 	}
 
+	pthread_mutex_unlock(&port_map_mutex);
+
 	/* Out of sockets in our own PID namespace, what to do? FIXME */
 	return UINT_MAX;
 }
@@ -79,7 +88,10 @@ static void release_local_port(uint32_t port)
 		return;
 	
 	nr = port >> 22;
-	used_ports_map[nr / 32] &= ~(1 << nr % 32);
+
+	pthread_mutex_lock(&port_map_mutex);
+	used_ports_map[nr / 32] &= ~(1 << (nr % 32));
+	pthread_mutex_unlock(&port_map_mutex);
 }
 
 /**