diff --git a/mod_for_test_scripts/100setupTestingInterface b/mod_for_test_scripts/100setupTestingInterface
index 8c530ea5fa..cc3bb248ba 100755
--- a/mod_for_test_scripts/100setupTestingInterface
+++ b/mod_for_test_scripts/100setupTestingInterface
@@ -11,7 +11,9 @@ testif=eth_test
 # Prevent flimflam from taking control of the backchannel network device.
 ORIG_CONF=${ROOT_FS_DIR}/etc/init/flimflam.conf
 TEMP_CONF=${ORIG_CONF}.tmp
-sed "s,flimflamd,flimflamd -I ${testif}," ${ORIG_CONF} > ${TEMP_CONF}
+sed -e "s,flimflamd,flimflamd -I ${testif}," \
+    -e "s,SHILL_TEST_ARGS=\"\",SHILL_TEST_ARGS=\"--device-black-list=${testif}\"," \
+    ${ORIG_CONF} > ${TEMP_CONF}
 mv -f ${TEMP_CONF} ${ORIG_CONF}
 
 # Arrange to run dhclient on the backchannel device but without