diff --git a/pipenv/cmdparse.py b/pipenv/cmdparse.py
index d7e349da..6240f0ba 100644
--- a/pipenv/cmdparse.py
+++ b/pipenv/cmdparse.py
@@ -35,7 +35,7 @@ class Script(object):
     def extend(self, extra_args):
         self._parts.extend(extra_args)
 
-    def cmdify(self, extra_args=None):
+    def cmdify(self):
         """Encode into a cmd-executable string.
 
         This re-implements CreateProcess's quoting logic to turn a list of
@@ -54,8 +54,6 @@ class Script(object):
 
         See also: https://docs.python.org/3/library/subprocess.html#converting-argument-sequence
         """
-        if extra_args:
-            self.extend(extra_args)
         return ' '.join(
             '"{0}"'.format(re.sub(r'(\\*)"', r'\1\1\\"', arg))
             for arg in self._parts
diff --git a/tests/test_cmdparse.py b/tests/test_cmdparse.py
index 4e72ac5b..f54a276a 100644
--- a/tests/test_cmdparse.py
+++ b/tests/test_cmdparse.py
@@ -12,12 +12,20 @@ def test_parse():
     assert script.args == ['-c', "print('hello')"], script
 
 
+@pytest.mark.run
+def test_extend():
+    script = Script.parse(['python', '-c', "print('hello')"])
+    script.extend(['--verbose'])
+    assert script.command == 'python'
+    assert script.args == ['-c', "print('hello')", "--verbose"], script
+
+
 @pytest.mark.run
 @pytest.mark.script
 def test_cmdify():
     script = Script.parse(['python', '-c', "print('hello')"])
-    cmd = script.cmdify(['--verbose'])
-    assert cmd == '"python" "-c" "print(\'hello\')" "--verbose"', script
+    cmd = script.cmdify()
+    assert cmd == '"python" "-c" "print(\'hello\')"', script
 
 
 @pytest.mark.run
@@ -27,7 +35,7 @@ def test_cmdify_complex():
         '"C:\\Program Files\\Python36\\python.exe" -c',
         """ "print(\'Double quote: \\\"\')" """.strip(),
     ]))
-    assert script.cmdify([]) == ' '.join([
+    assert script.cmdify() == ' '.join([
         '"C:\\Program Files\\Python36\\python.exe"',
         '"-c"',
         """ "print(\'Double quote: \\\"\')" """.strip(),