diff --git a/artiq/gateware/dsp/sawg.py b/artiq/gateware/dsp/sawg.py
index 28549611c..0d038e4fc 100644
--- a/artiq/gateware/dsp/sawg.py
+++ b/artiq/gateware/dsp/sawg.py
@@ -147,7 +147,7 @@ class Channel(Module, SatAddMixin):
         self.submodules.a1 = a1 = SplineParallelDDS(widths, orders)
         self.submodules.a2 = a2 = SplineParallelDDS(widths, orders)
         self.submodules.b = b = SplineParallelDUC(
-            widths._replace(a=len(a1.xo[0])), orders,
+            widths._replace(a=len(a1.xo[0]), f=widths.f - width), orders,
             parallelism=parallelism, a_delay=-a1.latency)
         cfg = Config(widths.a)
         u = Spline(width=widths.a, order=orders.a)