diff --git a/autoninja b/autoninja
index 76fee587b..45c71fc64 100755
--- a/autoninja
+++ b/autoninja
@@ -14,7 +14,8 @@ fi
 
 # Execute whatever is printed by autoninja.py.
 # Also print it to reassure that the right settings are being used.
-command=$(vpython "$(dirname -- "$0")/autoninja.py" "$@")
+# Don't use python3 because it doesn't work in git bash on Windows.
+command=$(python "$(dirname -- "$0")/autoninja.py" "$@")
 if [ "$NINJA_SUMMARIZE_BUILD" == "1" ]; then
   echo "$command"
 fi
diff --git a/autoninja.bat b/autoninja.bat
index b5bac5788..34b477e71 100755
--- a/autoninja.bat
+++ b/autoninja.bat
@@ -5,8 +5,10 @@
 
 setlocal
 
+set scriptdir=%~dp0
+
 REM Set unique build ID.
-FOR /f "usebackq tokens=*" %%a in (`python3 -c "import uuid; print(uuid.uuid4())"`) do set AUTONINJA_BUILD_ID=%%a
+FOR /f "usebackq tokens=*" %%a in (`python -c "import uuid; print(uuid.uuid4())"`) do set AUTONINJA_BUILD_ID=%%a
 
 REM If a build performance summary has been requested then also set NINJA_STATUS
 REM to trigger more verbose status updates. In particular this makes it possible
@@ -14,8 +16,6 @@ REM to see how quickly process creation is happening - often a critical clue on
 REM Windows. The trailing space is intentional.
 if "%NINJA_SUMMARIZE_BUILD%" == "1" set NINJA_STATUS=[%%r processes, %%f/%%t @ %%o/s : %%es ] 
 
-set scriptdir=%~dp0
-
 :loop
 IF NOT "%1"=="" (
     @rem Tell goma or reclient to not do network compiles.
@@ -33,17 +33,21 @@ IF NOT "%1"=="" (
 
 REM Execute whatever is printed by autoninja.py.
 REM Also print it to reassure that the right settings are being used.
-FOR /f "usebackq tokens=*" %%a in (`vpython %scriptdir%autoninja.py "%*"`) do echo %%a & %%a
+REM Don't use vpython - it is too slow to start.
+REM Don't use python3 because it doesn't work in git bash on Windows and we
+REM should be consistent between autoninja.bat and the autoninja script used by
+REM git bash.
+FOR /f "usebackq tokens=*" %%a in (`python %scriptdir%autoninja.py "%*"`) do echo %%a & %%a
 @if errorlevel 1 goto buildfailure
 
-REM Use call to invoke python script here, because we may use python3 via python3.bat.
-@if "%NINJA_SUMMARIZE_BUILD%" == "1" call python3 %scriptdir%post_build_ninja_summary.py %*
-@call python3 %scriptdir%ninjalog_uploader_wrapper.py --cmdline %*
+REM Use call to invoke python script here, because we use python via python.bat.
+@if "%NINJA_SUMMARIZE_BUILD%" == "1" call python %scriptdir%post_build_ninja_summary.py %*
+@call python %scriptdir%ninjalog_uploader_wrapper.py --cmdline %*
 
 exit /b
 :buildfailure
 
-@call python3 %scriptdir%ninjalog_uploader_wrapper.py --cmdline %*
+@call python %scriptdir%ninjalog_uploader_wrapper.py --cmdline %*
 
 REM Return an error code of 1 so that if a developer types:
 REM "autoninja chrome && chrome" then chrome won't run if the build fails.
diff --git a/autoninja.py b/autoninja.py
index 53f972ccc..3afdff68c 100755
--- a/autoninja.py
+++ b/autoninja.py
@@ -11,18 +11,12 @@ makes using remote build acceleration simpler and safer, and avoids errors that
 can cause slow goma builds or swap-storms on unaccelerated builds.
 """
 
-# [VPYTHON:BEGIN]
-# wheel: <
-#   name: "infra/python/wheels/psutil/${vpython_platform}"
-#   version: "version:5.6.2"
-# >
-# [VPYTHON:END]
-
 from __future__ import print_function
 
+import multiprocessing
 import os
-import psutil
 import re
+import subprocess
 import sys
 
 SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))
@@ -125,6 +119,25 @@ goma_disabled_env = os.environ.get('GOMA_DISABLED', '0').lower()
 if offline or goma_disabled_env in ['true', 't', 'yes', 'y', '1']:
   use_goma = False
 
+if use_goma:
+  gomacc_file = 'gomacc.exe' if sys.platform.startswith('win') else 'gomacc'
+  gomacc_path = os.path.join(SCRIPT_DIR, '.cipd_bin', gomacc_file)
+  # Don't invoke gomacc if it doesn't exist.
+  if os.path.exists(gomacc_path):
+    # Check to make sure that goma is running. If not, don't start the build.
+    status = subprocess.call([gomacc_path, 'port'], stdout=subprocess.PIPE,
+                             stderr=subprocess.PIPE, shell=False)
+    if status == 1:
+      print('Goma is not running. Use "goma_ctl ensure_start" to start it.',
+            file=sys.stderr)
+      if sys.platform.startswith('win'):
+        # Set an exit code of 1 in the batch file.
+        print('cmd /c exit 1')
+      else:
+        # Set an exit code of 1 by executing 'false' in the bash script.
+        print('false')
+      sys.exit(1)
+
 # Specify ninja.exe on Windows so that ninja.bat can call autoninja and not
 # be called back.
 ninja_exe = 'ninja.exe' if sys.platform.startswith('win') else 'ninja'
@@ -144,7 +157,7 @@ if (sys.platform.startswith('linux')
 # or fail to execute ninja if depot_tools is not in PATH.
 args = prefix_args + [ninja_exe_path] + input_args[1:]
 
-num_cores = psutil.cpu_count()
+num_cores = multiprocessing.cpu_count()
 if not j_specified and not t_specified:
   if use_goma or use_rbe:
     args.append('-j')
@@ -201,4 +214,3 @@ if offline and not sys.platform.startswith('win'):
   print('RBE_remote_disabled=1 GOMA_DISABLED=1 ' + ' '.join(args))
 else:
   print(' '.join(args))
-