diff --git a/src/PIL/MpoImagePlugin.py b/src/PIL/MpoImagePlugin.py
index 7ea1018bc..a55cce2ec 100644
--- a/src/PIL/MpoImagePlugin.py
+++ b/src/PIL/MpoImagePlugin.py
@@ -102,7 +102,7 @@ class MpoImageFile(JpegImagePlugin.JpegImageFile):
     def adopt(jpeg_instance, mpheader=None):
         """
         Transform the instance of JpegImageFile into
-        instance of MpoImageFile.
+        an instance of MpoImageFile.
         After the call, the JpegImageFile is extended
         to be an MpoImageFile.