diff --git a/mercurial/mdiff.py b/mercurial/mdiff.py
--- a/mercurial/mdiff.py
+++ b/mercurial/mdiff.py
@@ -8,7 +8,6 @@
 from i18n import _
 import bdiff, mpatch, util
 import re, struct, base85, zlib
-from node import hex, nullid
 
 def splitnewlines(text):
     '''like str.splitlines, but only split on newlines.'''
@@ -301,14 +300,6 @@ def _unidiff(t1, t2, l1, l2, opts=defaul
 
 def b85diff(to, tn):
     '''print base85-encoded binary diff'''
-    def gitindex(text):
-        if not text:
-            return hex(nullid)
-        l = len(text)
-        s = util.sha1('blob %d\0' % l)
-        s.update(text)
-        return s.hexdigest()
-
     def fmtline(line):
         l = len(line)
         if l <= 26:
@@ -324,17 +315,22 @@ def b85diff(to, tn):
             yield text[i:i + csize]
             i += csize
 
-    tohash = gitindex(to)
-    tnhash = gitindex(tn)
-    if tohash == tnhash:
-        return ""
+    if to is None:
+        to = ''
+    if tn is None:
+        tn = ''
+
+    if to == tn:
+        return ''
 
     # TODO: deltas
-    ret = ['index %s..%s\nGIT binary patch\nliteral %s\n' %
-           (tohash, tnhash, len(tn))]
+    ret = []
+    ret.append('GIT binary patch\n')
+    ret.append('literal %s\n' % len(tn))
     for l in chunk(zlib.compress(tn)):
         ret.append(fmtline(l))
     ret.append('\n')
+
     return ''.join(ret)
 
 def patchtext(bin):
diff --git a/mercurial/patch.py b/mercurial/patch.py
--- a/mercurial/patch.py
+++ b/mercurial/patch.py
@@ -10,7 +10,7 @@ import cStringIO, email.Parser, os, errn
 import tempfile, zlib, shutil
 
 from i18n import _
-from node import hex, short
+from node import hex, nullid, short
 import base85, mdiff, scmutil, util, diffhelpers, copies, encoding, error
 import context
 
@@ -1662,6 +1662,22 @@ def trydiff(repo, revs, ctx1, ctx2, modi
             header.append('old mode %s\n' % omode)
             header.append('new mode %s\n' % nmode)
 
+    def addindexmeta(meta, revs):
+        if opts.git:
+            i = len(revs)
+            if i==2:
+                meta.append('index %s..%s\n' % tuple(revs))
+            elif i==3:
+                meta.append('index %s,%s..%s\n' % tuple(revs))
+
+    def gitindex(text):
+        if not text:
+            return hex(nullid)
+        l = len(text)
+        s = util.sha1('blob %d\0' % l)
+        s.update(text)
+        return s.hexdigest()
+
     def diffline(a, b, revs):
         if opts.git:
             line = 'diff --git a/%s b/%s\n' % (a, b)
@@ -1763,6 +1779,8 @@ def trydiff(repo, revs, ctx1, ctx2, modi
                 header.insert(0, diffline(join(a), join(b), revs))
             if dodiff == 'binary':
                 text = mdiff.b85diff(to, tn)
+                if text:
+                    addindexmeta(header, [gitindex(to), gitindex(tn)])
             else:
                 text = mdiff.unidiff(to, date1,
                                     # ctx2 date may be dynamic