diff --git a/presubmit_canned_checks.py b/presubmit_canned_checks.py
index 09439fb883..ba8c3ed3dc 100755
--- a/presubmit_canned_checks.py
+++ b/presubmit_canned_checks.py
@@ -74,7 +74,7 @@ def CheckChangeHasNoTabs(input_api, output_api):
   """
   for f, line_num, line in input_api.RightHandSideLines():
     if '\t' in line:
-      return [output_api.PresubmitError(
+      return [output_api.PresubmitPromptWarning(
           "Found a tab character in %s, line %s" %
           (f.LocalPath(), line_num))]
   return []
@@ -103,14 +103,15 @@ def CheckLongLines(input_api, output_api, maxlen=80):
 def CheckTreeIsOpen(input_api, output_api, url, closed):
   """Checks that an url's content doesn't match a regexp that would mean that
   the tree is closed."""
+  assert(input_api.is_committing)
   try:
     connection = input_api.urllib2.urlopen(url)
     status = connection.read()
     connection.close()
     if input_api.re.match(closed, status):
       long_text = status + '\n' + url
-      return [output_api.PresubmitError("The tree is closed.",
-                                        long_text=long_text)]
+      return [output_api.PresubmitPromptWarning("The tree is closed.",
+                                                long_text=long_text)]
   except IOError:
     pass
   return []
diff --git a/tests/presubmit_unittest.py b/tests/presubmit_unittest.py
index 1b020260b9..fa7dd7e340 100755
--- a/tests/presubmit_unittest.py
+++ b/tests/presubmit_unittest.py
@@ -925,7 +925,7 @@ class CannedChecksUnittest(PresubmitTestsBase):
   def testCannedCheckChangeHasNoTabs(self):
     self.TestContent(presubmit_canned_checks.CheckChangeHasNoTabs,
                      'blah blah', 'blah\tblah',
-                     presubmit.OutputApi.PresubmitError)
+                     presubmit.OutputApi.PresubmitPromptWarning)
 
   def testCannedCheckLongLines(self):
     check = lambda x,y: presubmit_canned_checks.CheckLongLines(x, y, 10)
@@ -934,6 +934,7 @@ class CannedChecksUnittest(PresubmitTestsBase):
 
   def testCannedCheckTreeIsOpenOpen(self):
     input_api = self.MockInputApi()
+    input_api.is_committing = True
     connection = self.mox.CreateMockAnything()
     input_api.urllib2.urlopen('url_to_open').AndReturn(connection)
     connection.read().AndReturn('1')
@@ -945,6 +946,7 @@ class CannedChecksUnittest(PresubmitTestsBase):
 
   def testCannedCheckTreeIsOpenClosed(self):
     input_api = self.MockInputApi()
+    input_api.is_committing = True
     connection = self.mox.CreateMockAnything()
     input_api.urllib2.urlopen('url_to_closed').AndReturn(connection)
     connection.read().AndReturn('0')
@@ -954,7 +956,7 @@ class CannedChecksUnittest(PresubmitTestsBase):
         input_api, presubmit.OutputApi, url='url_to_closed', closed='0')
     self.assertEquals(len(results), 1)
     self.assertEquals(results[0].__class__,
-                      presubmit.OutputApi.PresubmitError)
+                      presubmit.OutputApi.PresubmitPromptWarning)
 
   def testRunPythonUnitTestsNoTest(self):
     input_api = self.MockInputApi()