diff --git a/git_cl.py b/git_cl.py
index 62f339d9a3..21ade2a28e 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -150,6 +150,19 @@ def add_git_similarity(parser):
   parser.parse_args = Parse
 
 
+def is_dirty_git_tree(cmd):
+  # Make sure index is up-to-date before running diff-index.
+  RunGit(['update-index', '--refresh', '-q'], error_ok=True)
+  dirty = RunGit(['diff-index', '--name-status', 'HEAD'])
+  if dirty:
+    print 'Cannot %s with a dirty tree. You must commit locally first.' % cmd
+    print 'Uncommitted files: (git diff-index --name-status HEAD)'
+    print dirty[:4096]
+    if len(dirty) > 4096:
+      print '... (run "git diff-index --name-status HEAD" to see full output).'
+    return True
+  return False
+
 def MatchSvnGlob(url, base_url, glob_spec, allow_wildcards):
   """Return the corresponding git ref if |base_url| together with |glob_spec|
   matches the full |url|.
@@ -997,12 +1010,8 @@ def CMDpresubmit(parser, args):
                     help='Run checks even if tree is dirty')
   (options, args) = parser.parse_args(args)
 
-  # Make sure index is up-to-date before running diff-index.
-  RunGit(['update-index', '--refresh', '-q'], error_ok=True)
-  if not options.force and RunGit(['diff-index', 'HEAD']):
-    # TODO(maruel): Is this really necessary?
-    print ('Cannot presubmit with a dirty tree.\n'
-          'You must commit locally first (or use --force).')
+  if not options.force and is_dirty_git_tree('presubmit'):
+    print 'use --force to check even if tree is dirty.'
     return 1
 
   cl = Changelist()
@@ -1199,10 +1208,7 @@ def CMDupload(parser, args):
         'In the near future, -m or --message will send a message instead.\n'
         'See http://goo.gl/JGg0Z for details.\n')
 
-  # Make sure index is up-to-date before running diff-index.
-  RunGit(['update-index', '--refresh', '-q'], error_ok=True)
-  if RunGit(['diff-index', 'HEAD']):
-    print 'Cannot upload with a dirty tree.  You must commit locally first.'
+  if is_dirty_git_tree('upload'):
     return 1
 
   cl = Changelist()
@@ -1272,10 +1278,7 @@ def SendUpstream(parser, args, cmd):
   base_branch = args[0]
   base_has_submodules = IsSubmoduleMergeCommit(base_branch)
 
-  # Make sure index is up-to-date before running diff-index.
-  RunGit(['update-index', '--refresh', '-q'], error_ok=True)
-  if RunGit(['diff-index', 'HEAD']):
-    print 'Cannot %s with a dirty tree.  You must commit locally first.' % cmd
+  if is_dirty_git_tree(cmd):
     return 1
 
   # This rev-list syntax means "show all commits not in my branch that
diff --git a/tests/git_cl_test.py b/tests/git_cl_test.py
index 47e79395e6..148650497e 100755
--- a/tests/git_cl_test.py
+++ b/tests/git_cl_test.py
@@ -132,7 +132,7 @@ class TestGitCl(TestCase):
       ((['git', 'symbolic-ref', 'HEAD'],), 'master'),
       find_copies_call,
       ((['git', 'update-index', '--refresh', '-q'],), ''),
-      ((['git', 'diff-index', 'HEAD'],), ''),
+      ((['git', 'diff-index', '--name-status', 'HEAD'],), ''),
       ((['git', 'symbolic-ref', 'HEAD'],), 'master'),
       ((['git', 'config', 'branch.master.merge'],), 'master'),
       ((['git', 'config', 'branch.master.remote'],), 'origin'),
@@ -185,7 +185,7 @@ class TestGitCl(TestCase):
          '--grep=^SVN changes up to revision [0-9]*$',
          'refs/remotes/origin/master^!'],), ''),
       ((['git', 'update-index', '--refresh', '-q'],), ''),
-      ((['git', 'diff-index', 'HEAD'],), ''),
+      ((['git', 'diff-index', '--name-status', 'HEAD'],), ''),
       ((['git', 'rev-list', '^refs/heads/working',
          'refs/remotes/origin/master'],),
          ''),
@@ -415,7 +415,7 @@ class TestGitCl(TestCase):
         ((['git', 'config', '--int', '--get',
           'branch.master.git-find-copies'],), ''),
         ((['git', 'update-index', '--refresh', '-q'],), ''),
-        ((['git', 'diff-index', 'HEAD'],), ''),
+        ((['git', 'diff-index', '--name-status', 'HEAD'],), ''),
         ((['git', 'symbolic-ref', 'HEAD'],), 'master'),
         ((['git', 'config', 'branch.master.merge'],), 'master'),
         ((['git', 'config', 'branch.master.remote'],), 'origin'),