diff --git a/CHANGES.txt b/CHANGES.txt
index 7c014b077..348785fe8 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -2,6 +2,7 @@ v0.5.0, 2015-??-?? -- ???
  * jobs:
    * mr() no longer takes positional arguments (#814)
    * removed jar() (use mrjob.step.JarStep)
+   * JarStep() only takes "args" and "main_class" keyword args
    * removed testing methods parse_counters() and parse_output()
  * runners:
    * All runners:
diff --git a/mrjob/step.py b/mrjob/step.py
index 0964eaab0..b0841f6a7 100644
--- a/mrjob/step.py
+++ b/mrjob/step.py
@@ -32,9 +32,12 @@
 
 # params to specify how to run the step. need at least one of these
 _JOB_STEP_FUNC_PARAMS = _MAPPER_FUNCS + _COMBINER_FUNCS + _REDUCER_FUNCS
-# all allowable step params
+# all allowable MRStep params
 _JOB_STEP_PARAMS = _JOB_STEP_FUNC_PARAMS + _HADOOP_OPTS
 
+# all allowable JarStep constructor keyword args
+_JAR_STEP_KWARGS = ['args', 'main_class']
+
 
 log = logging.getLogger(__name__)
 
@@ -91,8 +94,8 @@ def __init__(self, **kwargs):
         # limit which keyword args can be specified
         bad_kwargs = sorted(set(kwargs) - set(_JOB_STEP_PARAMS))
         if bad_kwargs:
-            raise TypeError(
-                'mr() got an unexpected keyword argument %r' % bad_kwargs[0])
+            raise TypeError('MRStep() got an unexpected keyword argument %r' %
+                            bad_kwargs[0])
 
         if not set(kwargs) & set(_JOB_STEP_FUNC_PARAMS):
             raise ValueError("Step has no mappers and no reducers")
@@ -253,8 +256,7 @@ class JarStep(object):
     #: with the step's output path
     OUTPUT = '<output>'
 
-    # in v0.5.0, replace "*args" with "jar"
-    def __init__(self, *args, **kwargs):
+    def __init__(self, jar, **kwargs):
         """Define a Java JAR step.
 
         Accepts the following keyword arguments:
@@ -267,35 +269,19 @@ def __init__(self, *args, **kwargs):
                            in the jar's manifest file.
         :param args: (optional) A list of arguments to the jar
 
+        *jar* can also be passed as a positional argument
+
         See :ref:`non-hadoop-streaming-jar-steps` for sample usage.
         """
-        if args:
-            self._init_deprecated(*args, **kwargs)
-        else:
-            self._init_kwargs(**kwargs)
-
-    def _init_deprecated(
-            self, name, jar, main_class=None, step_args=None, args=None):
-        log.warning('Positional arguments to JarStep() (other than'
-                    ' jar) are deprecated and will be removed in v0.5.0')
+        bad_kwargs = sorted(set(kwargs) - set(_JAR_STEP_KWARGS))
+        if bad_kwargs:
+            raise TypeError('JarStep() got an unexpected keyword argument %r' %
+                            bad_kwargs[0])
 
         self.jar = jar
-        self.main_class = main_class
-        self.args = args or step_args or []
-
-    def _init_kwargs(
-            self, jar, main_class=None, args=None, step_args=None, name=None):
-        # deprecated arguments
-        if step_args:
-            log.warning('step_args argument to JarStep() has been'
-                        ' renamed to args, and will be removed in v0.5.0')
-        if name:
-            log.warning('name argument to JarStep() has no effect, and will'
-                        ' be removed in v0.5.0')
 
-        self.jar = jar
-        self.main_class = main_class
-        self.args = args or step_args or []
+        self.args = kwargs.get('args') or []
+        self.main_class = kwargs.get('main_class')
 
     def __repr__(self):
         repr_args = []
diff --git a/tests/test_step.py b/tests/test_step.py
index 1f4b6a194..e34d00c90 100644
--- a/tests/test_step.py
+++ b/tests/test_step.py
@@ -60,40 +60,6 @@ def test_some(self):
         self.assertEqual(JarStep(**kwargs).description(0), expected)
 
 
-class JarStepDeprecatedArgumentsTestCase(TestCase):
-
-    def test_positional(self):
-        with logger_disabled('mrjob.step'):
-            self.assertEqual(
-                JarStep('foo', 'bell.jar', 'First', ['one', '2']),
-                JarStep(jar='bell.jar', main_class='First', args=['one', '2'])
-            )
-
-    def test_mixed(self):
-        with logger_disabled('mrjob.step'):
-            self.assertEqual(
-                JarStep('foo', jar='bell.jar', args=['3', 'four']),
-                JarStep(jar='bell.jar', args=['3', 'four'])
-            )
-
-    def test_step_args_kwarg(self):
-        with logger_disabled('mrjob.step'):
-            self.assertEqual(
-                JarStep(jar='bell.jar', step_args=['5', 'six']),
-                JarStep(jar='bell.jar', args=['5', 'six'])
-            )
-
-    def test_name_kwarg(self):
-        with logger_disabled('mrjob.step'):
-            self.assertEqual(
-                JarStep(jar='pickle.jar', name='Bubbies'),
-                JarStep(jar='pickle.jar')
-            )
-
-    def test_bad_kwarg(self):
-        self.assertRaises(TypeError, JarStep, foo='bar')
-
-
 class MRStepInitTestCase(TestCase):
 
     ### Basic behavior ###