diff --git a/run_tests.sh b/run_tests.sh
index ccb843f38a..397d3cc814 100755
--- a/run_tests.sh
+++ b/run_tests.sh
@@ -68,6 +68,10 @@ function run_tests {
 
 function run_flake8 {
   echo "Running flake8 ..."
+  if [ $never_venv -eq 1 ]; then
+      echo "**WARNING**:" >&2
+      echo "Running flake8 without virtual env may miss OpenStack HACKING detection" >&2
+  fi
 
   ${wrapper} flake8
 }