diff --git a/overlay/etc/udev/rules.d/79-et-digirig-dr891.rules b/overlay/etc/udev/rules.d/79-et-digirig-dr891.rules
index fe2f725..62f39b6 100644
--- a/overlay/etc/udev/rules.d/79-et-digirig-dr891.rules
+++ b/overlay/etc/udev/rules.d/79-et-digirig-dr891.rules
@@ -11,30 +11,27 @@
 # 2. /dev/et-audio created
 # 3. rigctld is started
 # 
+# CAUTION: The FT-891 is an experimental device that may impact the stability of the platform and may
+#          not work 100% of the time. This device support is best effort only.
 
-# Ensure that the FT-891 is set as the current radio configuration.
-# If it is, set ET_DEVICE=FT-891 to allow following rules to match.
-SUBSYSTEM=="tty|sound", PROGRAM="/opt/emcomm-tools/sbin/udev-tester.sh yaesu-ft891", \
+# Special rule to ensure that the first serial interface (/dev/ttyUSB4) is tagged as ET_DEVICE=FT-891 so
+# that it can be used in the next CAT control rule. The second serial device will not work (/dev/ttyUSB5)
+# if it is incorrectly detected as the /dev/et-cat device.
+KERNEL=="ttyUSB[0-9]*", SUBSYSTEM=="tty", PROGRAM="/opt/emcomm-tools/sbin/udev-tester.sh yaesu-ft891", \
+    ATTRS{bInterfaceNumber}=="00", \
     ENV{ET_DEVICE}="FT-891"
 
-SUBSYSTEMS=="usb", ENV{ET_DEVICE}=="FT-891", ATTRS{bInterfaceProtocol}=="00", \
-    ACTION=="add", \
-    ENV{ET_FIRST_CAT_DEVICE}="yes"
-
 # CAT control device will only match if PROGRAM above matches (exit status=0)
-SUBSYSTEM=="tty", ENV{ET_DEVICE}=="FT-891", ENV{ET_FIRST_CAT_DEVICE}="yes", \
+SUBSYSTEM=="tty", ENV{ET_DEVICE}=="FT-891", \
     ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea70",\
     ACTION=="add", \
     ENV{ET_SUBDEVICE}="CAT", GROUP="dialout", MODE="0660", SYMLINK+="et-cat", \
     RUN+="/usr/bin/systemctl start rigctld"
 
-#SUBSYSTEMS=="usb", SUBSYSTEM=="tty", ENV{ET_DEVICE}=="FT-891", ATTRS{bInterfaceProtocol}=="00", \
-#    ACTION=="add", \
-#    ENV{ET_SUBDEVICE}="CAT", GROUP="dialout", MODE="0660", SYMLINK+="et-cat", \
-#    RUN+="/usr/bin/systemctl start rigctld"
-
 # Audio device will only match if PROGRAM above matches (exit status=0)
-SUBSYSTEM=="sound", ENV{ET_DEVICE}=="FT-891", ATTRS{idVendor}=="0d8c", ATTRS{idProduct}=="0012", \
+SUBSYSTEM=="sound", ATTRS{idVendor}=="0d8c", ATTRS{idProduct}=="0012", \
+    PROGRAM="/opt/emcomm-tools/sbin/udev-tester.sh yaesu-ft891", \
     ACTION=="add", \
+    ENV{ET_DEVICE}="FT-891", \
     ATTR{id}="ET_AUDIO", \
     ENV{ET_SUBDEVICE}="AUDIO", GROUP="audio", MODE="0660", SYMLINK+="et-audio"