diff --git a/sdkconfig.defaults b/sdkconfig.defaults
index 9d5270c..05407f4 100644
--- a/sdkconfig.defaults
+++ b/sdkconfig.defaults
@@ -16,3 +16,6 @@ CONFIG_ESP32P4_REV_MIN_100=y
 # 32 MB flash (esptool flash_id: GigaDevice c8/4019). App slots stay below 16 MB;
 # cache mapping above 16 MB is experimental in IDF.
 CONFIG_ESPTOOLPY_FLASHSIZE_32MB=y
+
+# LLDP and PTP send raw frames from their own tasks next to lwIP: serialise EMAC transmits
+CONFIG_ETH_TRANSMIT_MUTEX=y