diff --git a/src/asm/rgbasm.1 b/src/asm/rgbasm.1
index f5e6ab08..2d45084e 100644
--- a/src/asm/rgbasm.1
+++ b/src/asm/rgbasm.1
@@ -25,6 +25,7 @@
 .Op Fl D Ar name Ns Op = Ns Ar value
 .Op Fl g Ar chars
 .Op Fl i Ar path
+.Op Fl M Ar dependfile
 .Op Fl o Ar outfile
 .Op Fl p Ar pad_value
 .Ar file