Index: rts/System/Platform/Threading.h
--- rts/System/Platform/Threading.h.orig
+++ rts/System/Platform/Threading.h
@@ -12,6 +12,9 @@
 #ifdef __APPLE__
 #include <libkern/OSAtomic.h> // OSAtomicIncrement64
 #endif
+#ifdef __OpenBSD__
+#include <pthread_np.h>
+#endif
 
 #include "System/Platform/Win/win32.h"
 #include "System/Threading/SpringThreading.h"
