diff --git a/tempest/cmd/run.py b/tempest/cmd/run.py
index 236953c..5fa8b74 100644
--- a/tempest/cmd/run.py
+++ b/tempest/cmd/run.py
@@ -135,6 +135,12 @@
             workspace_mgr = workspace.WorkspaceManager(
                 parsed_args.workspace_path)
             path = workspace_mgr.get_workspace(parsed_args.workspace)
+            if not path:
+                sys.exit(
+                    "The %r workspace isn't registered in "
+                    "%r. Use 'tempest init' to "
+                    "register the workspace." %
+                    (parsed_args.workspace, workspace_mgr.path))
             os.chdir(path)
             # NOTE(mtreinish): tempest init should create a .testrepository dir
             # but since workspaces can be imported let's sanity check and
diff --git a/tempest/cmd/workspace.py b/tempest/cmd/workspace.py
index b36cf4e..3c58648 100644
--- a/tempest/cmd/workspace.py
+++ b/tempest/cmd/workspace.py
@@ -72,7 +72,10 @@
 
     @lockutils.synchronized('workspaces', external=True)
     def get_workspace(self, name):
-        """Returns the workspace that has the given name"""
+        """Returns the workspace that has the given name
+
+        If the workspace isn't registered then `None` is returned.
+        """
         self._populate()
         return self.workspaces.get(name)
 
diff --git a/tempest/tests/cmd/test_run.py b/tempest/tests/cmd/test_run.py
index 772391f..7ac347d 100644
--- a/tempest/tests/cmd/test_run.py
+++ b/tempest/tests/cmd/test_run.py
@@ -18,6 +18,7 @@
 import subprocess
 import tempfile
 
+import fixtures
 import mock
 
 from tempest.cmd import run
@@ -122,3 +123,32 @@
         # too.
         subprocess.call(['git', 'init'], stderr=DEVNULL)
         self.assertRunExit(['tempest', 'run'], 1)
+
+
+class TestTakeAction(base.TestCase):
+    def test_workspace_not_registered(self):
+        class Exception_(Exception):
+            pass
+
+        m_exit = self.useFixture(fixtures.MockPatch('sys.exit')).mock
+        # sys.exit must not continue (or exit)
+        m_exit.side_effect = Exception_
+
+        workspace = self.getUniqueString()
+
+        tempest_run = run.TempestRun(app=mock.Mock(), app_args=mock.Mock())
+        parsed_args = mock.Mock()
+        parsed_args.config_file = []
+
+        # Override $HOME so that empty workspace gets created in temp dir.
+        self.useFixture(fixtures.TempHomeDir())
+
+        # Force use of the temporary home directory.
+        parsed_args.workspace_path = None
+
+        # Simulate --workspace argument.
+        parsed_args.workspace = workspace
+
+        self.assertRaises(Exception_, tempest_run.take_action, parsed_args)
+        exit_msg = m_exit.call_args[0][0]
+        self.assertIn(workspace, exit_msg)