diff --git a/man/man3/quaternion.3 b/man/man3/quaternion.3
index 31f4ab5..941df24 100644
--- a/man/man3/quaternion.3
+++ b/man/man3/quaternion.3
@@ -146,7 +146,7 @@
 This is just a rotation about the same axis by half the angle.
 .PD
 .SH SOURCE
-.B /usr/local/plan9/src/libgeometry/quaternion.c
+.B \*9/src/libgeometry/quaternion.c
 .SH SEE ALSO
 .IR matrix (3),
 .IR qball (3)