use macro for /usr/local/plan9
diff --git a/man/man3/mach-symbol.3 b/man/man3/mach-symbol.3
index c74ae8e..e14a7b2 100644
--- a/man/man3/mach-symbol.3
+++ b/man/man3/mach-symbol.3
@@ -369,7 +369,7 @@
 in the system error buffer where it is available via
 .IR errstr .
 .SH SOURCE
-.B /usr/local/plan9/src/libmach
+.B \*9/src/libmach
 .SH "SEE ALSO"
 .IR mach (3),
 .IR mach-file (3),