diff --git a/dev b/dev
index 9f66cbafc..f9fcb95e6 100755
--- a/dev
+++ b/dev
@@ -1,11 +1,11 @@
 #!/bin/sh
 VENV=../venv.mitmproxy
 
-virtualenv $VENV
+virtualenv $VENV || { echo 'virtualenv is not installed. Exiting.' ; exit 1; }
 source $VENV/bin/activate
 pip install --src .. -r requirements.txt
 
 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."
diff --git a/dev.bat b/dev.bat
index 303c804e1..82bdd0d4a 100644
--- a/dev.bat
+++ b/dev.bat
@@ -1,11 +1,11 @@
 @echo off
 set VENV=..\venv.mitmproxy
 
-virtualenv %VENV%
+virtualenv %VENV% || echo virtualenv is not installed.  Exiting.
 call %VENV%\Scripts\activate.bat
 pip install --src .. -r requirements.txt
 
 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.