diff --git a/src/calibre/ebooks/metadata/epub.py b/src/calibre/ebooks/metadata/epub.py
index 27fa94e217..30fe53f1a2 100644
--- a/src/calibre/ebooks/metadata/epub.py
+++ b/src/calibre/ebooks/metadata/epub.py
@@ -16,6 +16,7 @@ from calibre.ebooks.metadata.opf2 import OPF
 from calibre.ptempfile import TemporaryDirectory, PersistentTemporaryFile
 from calibre import CurrentDir, walk
 from calibre.constants import isosx
+from calibre.utils.localization import lang_as_iso639_1
 
 class EPubException(Exception):
     pass
@@ -231,6 +232,15 @@ def set_metadata(stream, mi, apply_null=False, update_timestamp=False):
 
     for x in ('guide', 'toc', 'manifest', 'spine'):
         setattr(mi, x, None)
+    if mi.languages:
+        langs = []
+        for lc in mi.languages:
+            lc2 = lang_as_iso639_1(lc)
+            if lc2: lc = lc2
+            langs.append(lc)
+        mi.languages = langs
+
+
     reader.opf.smart_update(mi)
     if apply_null:
         if not getattr(mi, 'series', None):
diff --git a/src/calibre/ebooks/oeb/output.py b/src/calibre/ebooks/oeb/output.py
index 816fe71abb..38ac2495fd 100644
--- a/src/calibre/ebooks/oeb/output.py
+++ b/src/calibre/ebooks/oeb/output.py
@@ -43,6 +43,7 @@ class OEBOutput(OutputFormatPlugin):
                         except:
                             self.log.exception('Something went wrong while trying to'
                                     ' workaround Pocketbook cover bug, ignoring')
+                        self.migrate_lang_code(root)
                     raw = etree.tostring(root, pretty_print=True,
                             encoding='utf-8', xml_declaration=True)
                     if key == OPF_MIME:
@@ -104,3 +105,12 @@ class OEBOutput(OutputFormatPlugin):
             p.remove(m)
             p.insert(0, m)
     # }}}
+
+    def migrate_lang_code(self, root): # {{{
+        from calibre.utils.localization import lang_as_iso639_1
+        for lang in root.xpath('//*[local-name() = "language"]'):
+            clc = lang_as_iso639_1(lang.text)
+            if clc:
+                lang.text = clc
+    # }}}
+