diff --git a/RELEASE_NOTES.rst b/RELEASE_NOTES.rst
index 0f4327e01..89bc0a463 100644
--- a/RELEASE_NOTES.rst
+++ b/RELEASE_NOTES.rst
@@ -51,6 +51,7 @@ Release notes
 * The PDQ(2/3) driver has been removed and is now being maintained out-of tree
   at https://github.com/m-labs/pdq. All SPI/USB driver layers, Mediator,
   CompoundPDQ and examples/documentation has been moved.
+* The master now rotates log files at midnight, rather than based on log size.
 
 
 2.4
diff --git a/artiq/master/log.py b/artiq/master/log.py
index f956dc7e1..581e009b2 100644
--- a/artiq/master/log.py
+++ b/artiq/master/log.py
@@ -27,11 +27,9 @@ def log_args(parser):
     group.add_argument("--log-file", default="",
                        help="store logs in rotated files; set the "
                             "base filename")
-    group.add_argument("--log-max-size", type=int, default=1024,
-                       help="maximum size of each log file in KiB "
-                            "(default: %(default)d)")
-    group.add_argument("--log-backup-count", type=int, default=6,
-                       help="number of old log files to keep (.<n> is added "
+    group.add_argument("--log-backup-count", type=int, default=0,
+                       help="number of old log files to keep, or 0 to keep "
+                            "all log files. '.<yy>-<mm>-<dd>' is added "
                             "to the base filename (default: %(default)d)")
 
 
@@ -47,9 +45,9 @@ def init_log(args):
     handlers.append(console_handler)
 
     if args.log_file:
-        file_handler = logging.handlers.RotatingFileHandler(
+        file_handler = logging.handlers.TimedRotatingFileHandler(
             args.log_file,
-            maxBytes=args.log_max_size*1024,
+            when="midnight",
             backupCount=args.log_backup_count)
         file_handler.setFormatter(logging.Formatter(
             "%(asctime)s %(levelname)s:%(source)s:%(name)s:%(message)s"))