diff --git a/unix/build-xorg-7.4 b/unix/build-xorg-7.4
index 4c0c57d..6f90661 100755
--- a/unix/build-xorg-7.4
+++ b/unix/build-xorg-7.4
@@ -6,7 +6,9 @@
 
 set -e
 
-PREFIX="/tmp/xorg-7.4-${USER}"
+if [ "$PREFIX" = "" ]; then
+	PREFIX="/tmp/xorg-7.4-${USER}"
+fi
 export ACLOCAL="aclocal -I ${PREFIX}/share/aclocal"
 export PKG_CONFIG_PATH="${PREFIX}/lib/pkgconfig"
 MAKE="make"