diff --git a/Lib/compileall.py b/Lib/compileall.py
index 40b148d..aa65c6b 100644
--- a/Lib/compileall.py
+++ b/Lib/compileall.py
@@ -49,7 +49,7 @@
 
 def compile_dir(dir, maxlevels=10, ddir=None, force=False, rx=None,
                 quiet=0, legacy=False, optimize=-1, workers=1,
-                invalidation_mode=py_compile.PycInvalidationMode.TIMESTAMP):
+                invalidation_mode=None):
     """Byte-compile all modules in the given directory tree.
 
     Arguments (only dir is required):
@@ -100,7 +100,7 @@
 
 def compile_file(fullname, ddir=None, force=False, rx=None, quiet=0,
                  legacy=False, optimize=-1,
-                 invalidation_mode=py_compile.PycInvalidationMode.TIMESTAMP):
+                 invalidation_mode=None):
     """Byte-compile one file.
 
     Arguments (only fullname is required):
@@ -186,7 +186,7 @@
 
 def compile_path(skip_curdir=1, maxlevels=0, force=False, quiet=0,
                  legacy=False, optimize=-1,
-                 invalidation_mode=py_compile.PycInvalidationMode.TIMESTAMP):
+                 invalidation_mode=None):
     """Byte-compile all module on sys.path.
 
     Arguments (all optional):
@@ -259,9 +259,12 @@
                         type=int, help='Run compileall concurrently')
     invalidation_modes = [mode.name.lower().replace('_', '-')
                           for mode in py_compile.PycInvalidationMode]
-    parser.add_argument('--invalidation-mode', default='timestamp',
+    parser.add_argument('--invalidation-mode',
                         choices=sorted(invalidation_modes),
-                        help='How the pycs will be invalidated at runtime')
+                        help=('set .pyc invalidation mode; defaults to '
+                              '"checked-hash" if the SOURCE_DATE_EPOCH '
+                              'environment variable is set, and '
+                              '"timestamp" otherwise.'))
 
     args = parser.parse_args()
     compile_dests = args.compile_dest
@@ -290,8 +293,11 @@
     if args.workers is not None:
         args.workers = args.workers or None
 
-    ivl_mode = args.invalidation_mode.replace('-', '_').upper()
-    invalidation_mode = py_compile.PycInvalidationMode[ivl_mode]
+    if args.invalidation_mode:
+        ivl_mode = args.invalidation_mode.replace('-', '_').upper()
+        invalidation_mode = py_compile.PycInvalidationMode[ivl_mode]
+    else:
+        invalidation_mode = None
 
     success = True
     try: