diff --git a/cocotbext/eth/gmii.py b/cocotbext/eth/gmii.py
index f7075a8..2cb1ed4 100644
--- a/cocotbext/eth/gmii.py
+++ b/cocotbext/eth/gmii.py
@@ -238,6 +238,8 @@ class GmiiSource(Reset):
                     self.queue_occupancy_bytes -= len(frame)
                     self.queue_occupancy_frames -= 1
                     frame.sim_time_start = get_sim_time()
+                    frame.sim_time_sfd = None
+                    frame.sim_time_end = None
                     self.log.info("TX frame: %s", frame)
                     frame.normalize()
 
diff --git a/cocotbext/eth/mii.py b/cocotbext/eth/mii.py
index cfe3c4b..a1c899f 100644
--- a/cocotbext/eth/mii.py
+++ b/cocotbext/eth/mii.py
@@ -139,6 +139,8 @@ class MiiSource(Reset):
                     self.queue_occupancy_bytes -= len(frame)
                     self.queue_occupancy_frames -= 1
                     frame.sim_time_start = get_sim_time()
+                    frame.sim_time_sfd = None
+                    frame.sim_time_end = None
                     self.log.info("TX frame: %s", frame)
                     frame.normalize()
 
diff --git a/cocotbext/eth/rgmii.py b/cocotbext/eth/rgmii.py
index 07ad7e6..228b97d 100644
--- a/cocotbext/eth/rgmii.py
+++ b/cocotbext/eth/rgmii.py
@@ -142,6 +142,8 @@ class RgmiiSource(Reset):
                     self.queue_occupancy_bytes -= len(frame)
                     self.queue_occupancy_frames -= 1
                     frame.sim_time_start = get_sim_time()
+                    frame.sim_time_sfd = None
+                    frame.sim_time_end = None
                     self.log.info("TX frame: %s", frame)
                     frame.normalize()
 
diff --git a/cocotbext/eth/xgmii.py b/cocotbext/eth/xgmii.py
index f22007c..5d77653 100644
--- a/cocotbext/eth/xgmii.py
+++ b/cocotbext/eth/xgmii.py
@@ -249,6 +249,8 @@ class XgmiiSource(Reset):
                         self.queue_occupancy_bytes -= len(frame)
                         self.queue_occupancy_frames -= 1
                         frame.sim_time_start = get_sim_time()
+                        frame.sim_time_sfd = None
+                        frame.sim_time_end = None
                         self.log.info("TX frame: %s", frame)
                         frame.normalize()
                         frame.start_lane = 0