diff --git a/engine/server/sv_sys_unix.c b/engine/server/sv_sys_unix.c
index 5e4ffac84..37c83bd09 100644
--- a/engine/server/sv_sys_unix.c
+++ b/engine/server/sv_sys_unix.c
@@ -36,6 +36,10 @@ Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 #include <errno.h>
 #include <fcntl.h>
 
+#ifdef MULTITHREAD
+#include <pthread.h>
+#endif
+
 // callbacks
 void Sys_Linebuffer_Callback (struct cvar_s *var, char *oldvalue);