diff --git a/presubmit_canned_checks.py b/presubmit_canned_checks.py
index 39c491f7c..f8a0a4eaa 100644
--- a/presubmit_canned_checks.py
+++ b/presubmit_canned_checks.py
@@ -528,11 +528,7 @@ def GetUnitTests(input_api, output_api, unit_tests, env=None):
 
   results = []
   for unit_test in unit_tests:
-    cmd = []
-    if input_api.platform == 'win32' and unit_test.endswith('.py'):
-      # Windows needs some help.
-      cmd = [input_api.python_executable]
-    cmd.append(unit_test)
+    cmd = [unit_test]
     if input_api.verbose:
       cmd.append('--verbose')
     kwargs = {'cwd': input_api.PresubmitLocalPath()}
diff --git a/presubmit_support.py b/presubmit_support.py
index 8493d273c..5b89a335d 100755
--- a/presubmit_support.py
+++ b/presubmit_support.py
@@ -438,8 +438,13 @@ class InputApi(object):
     self.unittest = unittest
     self.urllib2 = urllib2
 
-    # To easily fork python.
-    self.python_executable = sys.executable
+    self.is_windows = sys.platform == 'win32'
+
+    # Set python_executable to 'python'. This is interpreted in CallCommand to
+    # convert to vpython in order to allow scripts in other repos (e.g. src.git)
+    # to automatically pick up that repo's .vpython file, instead of inheriting
+    # the one in depot_tools.
+    self.python_executable = 'python'
     self.environ = os.environ
 
     # InputApi.platform is the platform you're currently running on.
@@ -468,7 +473,6 @@ class InputApi(object):
                                      fopen=file, os_path=self.os_path)
     self.owners_finder = owners_finder.OwnersFinder
     self.verbose = verbose
-    self.is_windows = sys.platform == 'win32'
     self.Command = CommandData
 
     # Replace <hash_map> and <hash_set> as headers that need to be included
@@ -1533,12 +1537,24 @@ def CallCommand(cmd_data):
   multiprocessing module.
 
   multiprocessing needs a top level function with a single argument.
+
+  This function converts invocation of .py files and invocations of "python" to
+  vpython invocations.
   """
+  vpython = 'vpython.bat' if sys.platform == 'win32' else 'vpython'
+
+  cmd = cmd_data.cmd
+  if cmd[0] == 'python':
+    cmd = list(cmd)
+    cmd[0] = vpython
+  elif cmd[0].endswith('.py'):
+    cmd = [vpython] + cmd
+
   cmd_data.kwargs['stdout'] = subprocess.PIPE
   cmd_data.kwargs['stderr'] = subprocess.STDOUT
   try:
     start = time.time()
-    (out, _), code = subprocess.communicate(cmd_data.cmd, **cmd_data.kwargs)
+    (out, _), code = subprocess.communicate(cmd, **cmd_data.kwargs)
     duration = time.time() - start
   except OSError as e:
     duration = time.time() - start
diff --git a/tests/presubmit_unittest.py b/tests/presubmit_unittest.py
index d9ac3e8fd..e94b5c7d9 100755
--- a/tests/presubmit_unittest.py
+++ b/tests/presubmit_unittest.py
@@ -2786,7 +2786,9 @@ class CannedChecksUnittest(PresubmitTestsBase):
     CommHelper(input_api, ['allo', '--verbose'], cwd=self.fake_root_dir)
     cmd = ['bar.py', '--verbose']
     if input_api.platform == 'win32':
-      cmd.insert(0, input_api.python_executable)
+      cmd.insert(0, 'vpython.bat')
+    else:
+      cmd.insert(0, 'vpython')
     CommHelper(input_api, cmd, cwd=self.fake_root_dir, ret=(('', None), 1))
 
     self.mox.ReplayAll()