diff --git a/bin/compile b/bin/compile
index e5d4fa40d8760a4d184edb8308b0dada49af37ac..8c99550ac5aa9fbbc5179cde5fa9d74cc7d21f88 100755
--- a/bin/compile
+++ b/bin/compile
@@ -33,12 +33,18 @@ if [ "$NAME" = "Python" ]; then
   [ -f manage.py ] && [ -f settings.py ] && { echo " !     Django app must be in a package subdirectory"; exit 1; }
 fi
 
-# reject a checked-in virtualenv
+# warn a checked-in virtualenv
 if [ -d "lib" ] || [ -d "bin" ]; then
   echo " !     You have a virtualenv checked in. You should ignore the appropriate paths in your repo. See http://devcenter.heroku.com/articles/gitignore for more info.";
+fi
+
+# reject a conflicting checked-in virtualenv
+if [ -f "lib/python2.7" ]; then
+  echo " !     Checked-in virtualenv conflict."
   exit 1;
 fi
 
+
 # copy artifacts out of cache if exists
 mkdir -p $CACHE_DIR
 for dir in $VIRTUALENV_DIRS; do