diff --git a/doc/changes/aux/mr.282.md b/doc/changes/aux/mr.282.md
new file mode 100644
index 000000000..b81956a95
--- /dev/null
+++ b/doc/changes/aux/mr.282.md
@@ -0,0 +1 @@
+threading: Fix missing `#pragma once` in `os/os_threading.h`.
diff --git a/src/xrt/auxiliary/os/os_threading.h b/src/xrt/auxiliary/os/os_threading.h
index 6714ea857..40d33ba7f 100644
--- a/src/xrt/auxiliary/os/os_threading.h
+++ b/src/xrt/auxiliary/os/os_threading.h
@@ -8,6 +8,8 @@
  * @ingroup aux_os
  */
 
+#pragma once
+
 #include "xrt/xrt_config_os.h"
 #include "util/u_misc.h"