diff --git a/artiq/gateware/targets/sayma_amc.py b/artiq/gateware/targets/sayma_amc.py
index 0dd27d30a..7a175f8fd 100755
--- a/artiq/gateware/targets/sayma_amc.py
+++ b/artiq/gateware/targets/sayma_amc.py
@@ -170,7 +170,7 @@ class Standalone(MiniSoC, AMPSoC):
 
         # AMC/RTM serwb
         serwb_pads = platform.request("amc_rtm_serwb")
-        serwb_phy_amc = serwb.phy.SERWBPHY(platform.device, serwb_pads, mode="master")
+        serwb_phy_amc = serwb.phy.SERWBPHY(platform.device, serwb_pads, mode="master", phy_width=4)
         self.submodules.serwb_phy_amc = serwb_phy_amc
         self.csr_devices.append("serwb_phy_amc")
 
diff --git a/artiq/gateware/targets/sayma_rtm.py b/artiq/gateware/targets/sayma_rtm.py
index 30981ed54..efd491b5d 100755
--- a/artiq/gateware/targets/sayma_rtm.py
+++ b/artiq/gateware/targets/sayma_rtm.py
@@ -156,7 +156,7 @@ class SaymaRTM(Module):
         # AMC/RTM serwb
         serwb_pads = platform.request("amc_rtm_serwb")
         platform.add_period_constraint(serwb_pads.clk_p, 10.)
-        serwb_phy_rtm = serwb.phy.SERWBPHY(platform.device, serwb_pads, mode="slave")
+        serwb_phy_rtm = serwb.phy.SERWBPHY(platform.device, serwb_pads, mode="slave", phy_width=4)
         self.submodules.serwb_phy_rtm = serwb_phy_rtm
         self.comb += self.crg.serwb_refclk.eq(serwb_phy_rtm.serdes.refclk)
         csr_devices.append("serwb_phy_rtm")