diff --git a/manifest_xml.py b/manifest_xml.py
index a7fe8dd..3ac607e 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -167,12 +167,13 @@
   def _ParseGroups(self, groups):
     return [x for x in re.split(r'[,\s]+', groups) if x]
 
-  def Save(self, fd, peg_rev=False, peg_rev_upstream=True):
+  def Save(self, fd, peg_rev=False, peg_rev_upstream=True, groups=None):
     """Write the current manifest out to the given file descriptor.
     """
     mp = self.manifestProject
 
-    groups = mp.config.GetString('manifest.groups')
+    if groups is None:
+      groups = mp.config.GetString('manifest.groups')
     if groups:
       groups = self._ParseGroups(groups)