diff --git a/etc/prefs.sh-EXAMPLE b/etc/prefs.sh-EXAMPLE
index c8c0e0de0..4b70b3aa0 100644
--- a/etc/prefs.sh-EXAMPLE
+++ b/etc/prefs.sh-EXAMPLE
@@ -160,8 +160,10 @@ export FOAM_VERBOSE=1
 # System installed bison
 #export BISON_SYSTEM=1
 
-# System installed flex
+# System installed flex. FLEX_DIR should point to the directory where
+# $FLEX_DIR/bin/flex is located
 #export FLEX_SYSTEM=1
+#export FLEX_DIR=/usr
 
 # System installed m4
 #export M4_SYSTEM=1