diff -r 339f9d93daa6 -r 5cb830801855 mercurial/merge.py
--- a/mercurial/merge.py	Wed Oct 12 12:22:18 2016 +0200
+++ b/mercurial/merge.py	Wed Oct 12 12:22:18 2016 +0200
@@ -478,7 +478,9 @@
             if fca.node() == nullid and flags != flo:
                 if preresolve:
                     self._repo.ui.warn(
-                        _('warning: cannot merge flags for %s\n') % afile)
+                        _('warning: cannot merge flags for %s '
+                          'without common ancestor - keeping local flags\n')
+                        % afile)
             elif flags == fla:
                 flags = flo
         if preresolve: