diff -up createrepo-0.9.9/modifyrepo.py.orig createrepo-0.9.9/modifyrepo.py
--- createrepo-0.9.9/modifyrepo.py.orig	2016-12-08 16:03:27.747862638 +0100
+++ createrepo-0.9.9/modifyrepo.py	2016-12-08 16:04:15.499625562 +0100
@@ -31,11 +31,12 @@ import sys
 from createrepo import __version__
 from createrepo.utils import checksum_and_rename, compressOpen, MDError
 from createrepo.utils import _available_compression
-from yum.misc import checksum
+from yum.misc import checksum, AutoFileChecksums
 
 from yum.repoMDObject import RepoMD, RepoMDError, RepoData
 from xml.dom import minidom
 from optparse import OptionParser
+from cStringIO import StringIO
 
 
 class RepoMetadata:
@@ -96,29 +97,29 @@ class RepoMetadata:
         if isinstance(metadata, minidom.Document):
             md = metadata.toxml()
             mdname = 'updateinfo.xml'
+            oldmd = AutoFileChecksums(StringIO(md), [self.checksum_type])
+            oldmd.read()
         elif isinstance(metadata, str):
             if os.path.exists(metadata):
-                if metadata.split('.')[-1] in ('gz', 'bz2', 'xz'):
+                mdname = os.path.basename(metadata)
+                if mdname.split('.')[-1] in ('gz', 'bz2', 'xz'):
+                    mdname = mdname.rsplit('.', 1)[0]
                     oldmd = compressOpen(metadata, mode='rb')
                 else:
                     oldmd = file(metadata, 'r')
+                oldmd = AutoFileChecksums(oldmd, [self.checksum_type])
                 md = oldmd.read()
                 oldmd.close()
-                mdname = os.path.basename(metadata)
             else:
                 raise MDError, '%s not found' % metadata
         else:
             raise MDError, 'invalid metadata type'
 
-        do_compress = False
         ## Compress the metadata and move it into the repodata
-        if self.compress and mdname.split('.')[-1] not in ('gz', 'bz2', 'xz'):
-            do_compress = True
-            mdname += '.' + self.compress_type
         mdtype = self._get_mdtype(mdname, mdtype)
-
         destmd = os.path.join(self.repodir, mdname)
-        if do_compress:
+        if self.compress:
+            destmd += '.' + self.compress_type
             newmd = compressOpen(destmd, mode='wb', compress_type=self.compress_type)
         else:
             newmd = open(destmd, 'wb')
@@ -127,7 +128,6 @@ class RepoMetadata:
         newmd.close()
         print "Wrote:", destmd
 
-        open_csum = checksum(self.checksum_type, metadata)
         if self.unique_md_filenames:
             csum, destmd = checksum_and_rename(destmd, self.checksum_type)
         else:
@@ -141,7 +141,7 @@ class RepoMetadata:
         new_rd.type = mdtype
         new_rd.location = (None, 'repodata/' + base_destmd)
         new_rd.checksum = (self.checksum_type, csum)
-        new_rd.openchecksum = (self.checksum_type, open_csum)
+        new_rd.openchecksum = (self.checksum_type, oldmd.checksums.hexdigests().popitem()[1])
         new_rd.size = str(os.stat(destmd).st_size)
         new_rd.timestamp = str(int(os.stat(destmd).st_mtime))
         self.repoobj.repoData[new_rd.type] = new_rd