diff --git a/lang/m2/comp/modula-2.1 b/lang/m2/comp/modula-2.1
index d3fd8400..8e093f12 100644
--- a/lang/m2/comp/modula-2.1
+++ b/lang/m2/comp/modula-2.1
@@ -84,6 +84,9 @@ make all procedure names global, so that \fIadb\fR(1) understands them.
 make INTEGER ranges symmetric, t.i., MIN(INTEGER) = - MAX(INTEGER).
 This is useful for interpreters that use the "real" MIN(INTEGER) to
 indicate "undefined".
+.IP \fB\-Xi\fR\fIn\fR
+set maximum number of bits in a set to \fIn\fP.
+When not used, a default value is retained.
 .LP
 .SH SEE ALSO
 \fIack\fR(1), \fIem_m2\fR(6)