diff --git a/src/PIL/MpoImagePlugin.py b/src/PIL/MpoImagePlugin.py
index 5b606b345..7ea1018bc 100644
--- a/src/PIL/MpoImagePlugin.py
+++ b/src/PIL/MpoImagePlugin.py
@@ -109,7 +109,7 @@ class MpoImageFile(JpegImagePlugin.JpegImageFile):
         This is essentially useful when opening a JPEG
         file that reveals itself as an MPO, to avoid
         double call to _open.
-        '''
+        """
         jpeg_instance.__class__ = MpoImageFile
         jpeg_instance._after_jpeg_open(mpheader)
         return jpeg_instance