diff --git a/dev b/dev
index 0860157ed..153aafd05 100755
--- a/dev
+++ b/dev
@@ -2,7 +2,7 @@
 set -e
 VENV=../venv.mitmproxy
 
-python -m virtualenv $VENV
+python -m virtualenv $VENV || { echo 'virtualenv is not installed. Exiting.' ; exit 1; }
 source $VENV/bin/activate
 pip install --src .. -r requirements.txt
 
diff --git a/dev.bat b/dev.bat
index 59e654d4a..dab9010ac 100644
--- a/dev.bat
+++ b/dev.bat
@@ -11,4 +11,4 @@ if %errorlevel% neq 0 exit /b %errorlevel%
 echo.
 echo * Created virtualenv environment in %VENV%.
 echo * Installed all dependencies into the virtualenv.
-echo * Activated virtualenv environment.
\ No newline at end of file
+echo * Activated virtualenv environment.