diff --git a/pretty_midi/pretty_midi.py b/pretty_midi/pretty_midi.py
index 9d65daa..614b857 100644
--- a/pretty_midi/pretty_midi.py
+++ b/pretty_midi/pretty_midi.py
@@ -57,8 +57,11 @@ def __init__(self, midi_file=None, resolution=220, initial_tempo=120.):
 
         """
         if midi_file is not None:
+            # File passed in is already loaded, just use it
+            if isinstance(midi_file, mido.MidiFile):
+                midi_data = midi_file
             # Load in the MIDI data using the midi module
-            if isinstance(midi_file, six.string_types):
+            elif isinstance(midi_file, six.string_types):
                 # If a string was given, pass it as the string filename
                 midi_data = mido.MidiFile(filename=midi_file)
             else: