diff --git a/libc/kernel/tools/update_all.py b/libc/kernel/tools/update_all.py
index 6272fcf..d25dc0e 100755
--- a/libc/kernel/tools/update_all.py
+++ b/libc/kernel/tools/update_all.py
@@ -73,7 +73,9 @@
 
     print "cleaning: %-*s -> %-*s (%s)" % ( 35, path, 35, dst_path, r )
 
-usePerforce = os.environ.has_key("ANDROID_PRODUCT_OUT")
+# We don't use Perforce anymore, but just in case, define ANDROID_USE_P4
+# in your environment if you think you need it.
+usePerforce = os.environ.has_key("ANDROID_USE_P4")
 
 if usePerforce:
     b.updateP4Files()