diff --git a/sys/sys/signal.h b/sys/sys/signal.h
index ac5fc5194a9b..9542cb1c9a94 100644
--- a/sys/sys/signal.h
+++ b/sys/sys/signal.h
@@ -111,6 +111,10 @@
 #define	SIGUSR1		30	/* user defined signal 1 */
 #define	SIGUSR2		31	/* user defined signal 2 */
 #endif
+/*
+ * XXX Should this follow any _VISIBLE tag?
+ */
+#define	SIGTHR		32	/* Thread interrupt. */
 /*
  * XXX missing SIGRTMIN, SIGRTMAX.
  */