Index: src/lib/OpenEXRCore/internal_thread.h
--- src/lib/OpenEXRCore/internal_thread.h.orig
+++ src/lib/OpenEXRCore/internal_thread.h
@@ -29,7 +29,7 @@ call_once (once_flag* flag, void (*func) (void))
 {
     InitOnceExecuteOnce (flag, once_init_fn, (PVOID) func, NULL);
 }
-#    elif __has_include(<threads.h>) && !defined(__FreeBSD__)
+#    elif __has_include(<threads.h>) && !defined(__FreeBSD__) && !defined(__OpenBSD__)
 /*
  * On Linux (glibc 2.28+), use standard <threads.h>.
  * FreeBSD requires -lstdthreads for <threads.h>; use pthread fallback instead.
