# Buggy code
def _get_new_index(self):
    """return our new index"""
    ax = self.ax
    ax_attrs = ax._get_attributes_dict()
    ax_attrs["freq"] = self.freq
    obj = self._selected_obj

    if len(ax) == 0:
        new_index = PeriodIndex(data=[], **ax_attrs)
        return obj.reindex(new_index)

    start = ax[0].asfreq(self.freq, how=self.convention)
    end = ax[-1].asfreq(self.freq, how="end")

    return period_range(start, end, **ax_attrs)


# Traceback (TypeError)
In [38]: pd.Series(1, index=pd.period_range(start='2000', periods=100)).resample('M').count()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-38-295afa97781f> in <module>()
----> 1 pd.Series(1, index=pd.period_range(start='2000', periods=100)).resample('M').count()

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in f(self, _method)
473
474     def f(self, _method=method):
--> 475         return self._groupby_and_aggregate(None, _method)
476     f.__doc__ = getattr(GroupBy, method).__doc__
477     setattr(Resampler, method, f)

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in _groupby_and_aggregate(self, grouper, how, *args, **kwargs)
353
354         if grouper is None:
--> 355             self._set_binner()
356             grouper = self.grouper
357

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in _set_binner(self)
202
203         if self.binner is None:
--> 204             self.binner, self.grouper = self._get_binner()
205
206     def _get_binner(self):

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in _get_binner(self)
210         """
211
--> 212         binner, bins, binlabels = self._get_binner_for_time()
213         bin_grouper = BinGrouper(bins, binlabels)
214         return binner, bin_grouper

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in _get_binner_for_time(self)
538         if self.kind == 'period':
539             return self.groupby._get_time_period_bins(self.ax)
--> 540         return self.groupby._get_time_bins(self.ax)
541
542     def _downsample(self, how, **kwargs):

/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/tseries/resample.py in _get_time_bins(self, ax)
905         if not isinstance(ax, DatetimeIndex):
906             raise TypeError('axis must be a DatetimeIndex, but got '
--> 907                             'an instance of %r' % type(ax).__name__)
908
909         if len(ax) == 0:

TypeError: axis must be a DatetimeIndex, but got an instance of 'PeriodIndex'

# Fixed code
def _get_new_index(self):
    """return our new index"""
    ax = self.ax

    if len(ax) == 0:
        values = []
    else:
        start = ax[0].asfreq(self.freq, how=self.convention)
        end = ax[-1].asfreq(self.freq, how="end")
        values = period_range(start, end, freq=self.freq).values

    return ax._shallow_copy(values, freq=self.freq)