diff --git a/src/PIL/MpoImagePlugin.py b/src/PIL/MpoImagePlugin.py
index 216ed9fbc..5b606b345 100644
--- a/src/PIL/MpoImagePlugin.py
+++ b/src/PIL/MpoImagePlugin.py
@@ -100,7 +100,7 @@ class MpoImageFile(JpegImagePlugin.JpegImageFile):
 
     @staticmethod
     def adopt(jpeg_instance, mpheader=None):
-        '''
+        """
         Transform the instance of JpegImageFile into
         instance of MpoImageFile.
         After the call, the JpegImageFile is extended