diff --git a/h/m2_traps.h b/h/m2_traps.h
index 78d99dec4..e06392927 100644
--- a/h/m2_traps.h
+++ b/h/m2_traps.h
@@ -7,3 +7,4 @@
 #define M2_FORCH	68	/* FOR-loop control variable changed */
 #define M2_UUVFL	69	/* cardinal underflow */
 #define M2_INTERNAL	70	/* internal error, should not happen */
+#define M2_UNIXSIG	71	/* unix signal */