diff --git a/pandas/src/period.pyx b/pandas/src/period.pyx
index 5565f25937394..956f066187ce8 100644
--- a/pandas/src/period.pyx
+++ b/pandas/src/period.pyx
@@ -469,6 +469,7 @@ def extract_ordinals(ndarray[object] values, freq):
         object p
 
     freqstr = Period._maybe_convert_freq(freq).freqstr
+    base_freq = frequencies.get_base_alias(freqstr)
 
     for i in range(n):
         p = values[i]
@@ -479,8 +480,9 @@ def extract_ordinals(ndarray[object] values, freq):
             try:
                 ordinals[i] = p.ordinal
 
-                if p.freqstr != freqstr:
-                    msg = _DIFFERENT_FREQ_INDEX.format(freqstr, p.freqstr)
+                p_base_freq = frequencies.get_base_alias(p.freqstr)
+                if p_base_freq != base_freq:
+                    msg = _DIFFERENT_FREQ_INDEX.format(base_freq, p_base_freq)
                     raise IncompatibleFrequency(msg)
 
             except AttributeError:
diff --git a/pandas/tests/plotting/test_series.py b/pandas/tests/plotting/test_series.py
index e752197c6ad77..01ba0d99ee472 100644
--- a/pandas/tests/plotting/test_series.py
+++ b/pandas/tests/plotting/test_series.py
@@ -802,6 +802,11 @@ def test_custom_business_day_freq(self):
 
         _check_plot_works(s.plot)
 
+    def test_non_standard_intervals(self):
+        idx = pd.period_range('2000-01-01', '2000-01-05', freq='6H')
+        s = Series(np.random.randn(len(idx)), index=idx)
+        _check_plot_works(s.plot)
+
 
 if __name__ == '__main__':
     nose.runmodule(argv=[__file__, '-vvs', '-x', '--pdb', '--pdb-failure'],