diff --git a/INSTALL b/INSTALL
index 60fcf1682..7f9e49000 100644
--- a/INSTALL
+++ b/INSTALL
@@ -164,6 +164,7 @@ The following script extends the demo_sift1M test to several types of
 indexes:
   
   export PYTHONPATH=.   # needed because the script is in a subdirectory
+  mkdir tmp             # some output will be written there
   python python/demo_auto_tune.py
 
 It will cycle through a few types of indexes and find optimal