use macro for /usr/local/plan9
diff --git a/man/man3/allocimage.3 b/man/man3/allocimage.3
index e9da53a..8bfd323 100644
--- a/man/man3/allocimage.3
+++ b/man/man3/allocimage.3
@@ -331,7 +331,7 @@
 	red = allocimage(display, Rect(0, 0, 1, 1), RGB24, 1, DRed);
 .EE
 .SH SOURCE
-.B /usr/local/plan9/src/libdraw
+.B \*9/src/libdraw
 .SH "SEE ALSO"
 .IR graphics (3),
 .IR draw (3),