diff --git a/caffeinate.py b/caffeinate.py
index 2e309dfa6d..e59e06f0b0 100644
--- a/caffeinate.py
+++ b/caffeinate.py
@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import contextlib
 import os
 import subprocess
 import sys
@@ -26,3 +27,33 @@ def call(args, **call_kwargs):
         else:
             args = ['caffeinate'] + args
     return subprocess.call(args, **call_kwargs)
+
+
+@contextlib.contextmanager
+def scope(actually_caffeinate=True):
+    """Acts as a context manager keeping a Mac awake, unless flagged off.
+
+    If the process is not running on a Mac, or `actually_caffeinate` is falsey,
+    this acts as a context manager that does nothing. The `actually_caffeinate`
+    flag is provided so command line flags can control the caffeinate behavior
+    without requiring weird plumbing to use or not use the context manager.
+
+    If running on a Mac while actually_caffeinate is True (the default), this
+    runs `caffeinate` in a separate process, which is terminated when the
+    context manager exits.
+    """
+    if sys.platform != 'darwin' or not actually_caffeinate:
+        # Behave like a no-op context manager.
+        yield False
+        return
+
+    cmd = ['caffeinate', '-i', '-w', str(os.getpid())]
+
+    proc = subprocess.Popen(cmd,
+                            stdin=subprocess.DEVNULL,
+                            stdout=subprocess.DEVNULL,
+                            stderr=subprocess.DEVNULL)
+    try:
+        yield True
+    finally:
+        proc.terminate()
diff --git a/fetch.py b/fetch.py
index 99ba59d16a..9614b65527 100755
--- a/fetch.py
+++ b/fetch.py
@@ -24,6 +24,7 @@ import shlex
 import subprocess
 import sys
 
+import caffeinate
 import gclient_utils
 import git_common
 
@@ -215,6 +216,13 @@ def handle_args(argv):
         type=str,
         default=None,
         help='Protocol to use to fetch dependencies, defaults to https.')
+    parser.add_argument(
+        '--caffeinate',
+        action=argparse.BooleanOptionalAction,
+        default=True,
+        help=('On macOS, prevent idle sleep during the operation. Enabled by'
+              ' default. Use --no-caffeinate to disable. No effect on other'
+              ' platforms.'))
 
     parser.add_argument('config',
                         type=str,
@@ -306,8 +314,9 @@ def run(options, spec, root):
 
 def main():
     args = handle_args(sys.argv)
-    spec, root = run_config_fetch(args.config, args.props)
-    return run(args, spec, root)
+    with caffeinate.scope(actually_caffeinate=args.caffeinate):
+        spec, root = run_config_fetch(args.config, args.props)
+        return run(args, spec, root)
 
 
 if __name__ == '__main__':
diff --git a/tests/fetch_test.py b/tests/fetch_test.py
index 5790487714..bf9277a865 100755
--- a/tests/fetch_test.py
+++ b/tests/fetch_test.py
@@ -49,6 +49,7 @@ class TestUtilityFunctions(unittest.TestCase):
                                force=False,
                                config='foo',
                                protocol_override=None,
+                               caffeinate=True,
                                props=[]), response)
 
         response = fetch.handle_args([
@@ -63,11 +64,13 @@ class TestUtilityFunctions(unittest.TestCase):
                                force=True,
                                config='foo',
                                protocol_override='sso',
+                               caffeinate=True,
                                props=['--some-param=1', '--bar=2']), response)
 
         response = fetch.handle_args([
             'filename', '-n', '--dry-run', '--no-hooks', '--nohistory',
-            '--force', '-p', 'sso', 'foo', '--some-param=1', '--bar=2'
+            '--force', '--no-caffeinate', '-p', 'sso', 'foo', '--some-param=1',
+            '--bar=2'
         ])
         self.assertEqual(
             argparse.Namespace(dry_run=True,
@@ -76,6 +79,7 @@ class TestUtilityFunctions(unittest.TestCase):
                                force=True,
                                config='foo',
                                protocol_override='sso',
+                               caffeinate=False,
                                props=['--some-param=1', '--bar=2']), response)
 
     @mock.patch('os.path.exists', return_value=False)