diff --git a/pipenv/cli.py b/pipenv/cli.py
index 615e3387..e53e48ce 100644
--- a/pipenv/cli.py
+++ b/pipenv/cli.py
@@ -868,6 +868,10 @@ def shell(three=None, python=False, compat=False, shell_args=None):
     # Ensure that virtualenv is available.
     ensure_project(three=three, python=python, validate=False)
 
+    if 'PIPENV_ACTIVE' in os.environ:
+        click.echo(crayons.yellow('Shell already activated. No action taken to avoid nested environments.'))
+        return
+
     # Set an environment variable, so we know we're in the environment.
     os.environ['PIPENV_ACTIVE'] = '1'