--- source/common/umutex.h-orig	2019-07-17 11:40:06.000000000 +0200
+++ source/common/umutex.h	2019-07-17 11:40:42.000000000 +0200
@@ -20,6 +20,18 @@
 #ifndef UMUTEX_H
 #define UMUTEX_H
 
+// Workaround for multithreading on XCode 9, see
+// https://github.com/tensorflow/tensorflow/issues/13220#issuecomment-331579775
+#ifdef __APPLE__
+#ifndef _MACH_PORT_T
+#define _MACH_PORT_T
+#include <sys/_types.h> /* __darwin_mach_port_t */
+typedef __darwin_mach_port_t mach_port_t;
+#include <pthread.h>
+mach_port_t pthread_mach_thread_np(pthread_t);
+#endif /* _MACH_PORT_T */
+#endif /* __APPLE__ */
+
 #include <atomic>
 #include <condition_variable>
 #include <mutex>