diff --git a/artiq/coredevice/ttl.py b/artiq/coredevice/ttl.py
index 09732fccc..4069c62aa 100644
--- a/artiq/coredevice/ttl.py
+++ b/artiq/coredevice/ttl.py
@@ -371,16 +371,17 @@ class TTLClockGen:
     The time cursor is not modified by any function in this class.
 
     :param channel: channel number
+    :param acc_width: accumulator width in bits
     """
     kernel_invariants = {"core", "channel", "acc_width"}
 
-    def __init__(self, dmgr, channel, core_device="core"):
+    def __init__(self, dmgr, channel, acc_width=24, core_device="core"):
         self.core = dmgr.get(core_device)
         self.channel = channel
 
         # in RTIO cycles
         self.previous_timestamp = numpy.int64(0)
-        self.acc_width = numpy.int64(24)
+        self.acc_width = numpy.int64(acc_width)
 
     @portable
     def frequency_to_ftw(self, frequency):