diff --git a/tests/08-ipv6/code/receiver/project-conf.h b/tests/08-ipv6/code/receiver/project-conf.h
index 118578620..3ac43a91c 100644
--- a/tests/08-ipv6/code/receiver/project-conf.h
+++ b/tests/08-ipv6/code/receiver/project-conf.h
@@ -1,7 +1,5 @@
-#undef UIP_CONF_ND6_SEND_NS
 #define UIP_CONF_ND6_SEND_NS 1
 
 #ifdef BUFSIZE
-#undef UIP_CONF_BUFFER_SIZE
 #define UIP_CONF_BUFFER_SIZE BUFSIZE
 #endif /* BUFSIZE */
diff --git a/tests/08-ipv6/code/sender/project-conf.h b/tests/08-ipv6/code/sender/project-conf.h
index 118578620..3ac43a91c 100644
--- a/tests/08-ipv6/code/sender/project-conf.h
+++ b/tests/08-ipv6/code/sender/project-conf.h
@@ -1,7 +1,5 @@
-#undef UIP_CONF_ND6_SEND_NS
 #define UIP_CONF_ND6_SEND_NS 1
 
 #ifdef BUFSIZE
-#undef UIP_CONF_BUFFER_SIZE
 #define UIP_CONF_BUFFER_SIZE BUFSIZE
 #endif /* BUFSIZE */
diff --git a/tests/13-ieee802154/code-flush-nbr-queue/project-conf.h b/tests/13-ieee802154/code-flush-nbr-queue/project-conf.h
index 662bfcd88..52b95b95c 100644
--- a/tests/13-ieee802154/code-flush-nbr-queue/project-conf.h
+++ b/tests/13-ieee802154/code-flush-nbr-queue/project-conf.h
@@ -35,17 +35,13 @@
 #define UNIT_TEST_PRINT_FUNCTION test_print_report
 
 /* Set the minimum value of QUEUEBUF_CONF_NUM for the flush_nbr_queue test */
-#undef QUEUEBUF_CONF_NUM
 #define QUEUEBUF_CONF_NUM   1
 
 /* TSCH per-slot logging */
-#undef TSCH_LOG_CONF_PER_SLOT
 #define TSCH_LOG_CONF_PER_SLOT 1
 
-#undef TSCH_CONF_AUTOSTART
 #define TSCH_CONF_AUTOSTART 1
 
-#undef TSCH_CONF_WITH_SIXTOP
 #define TSCH_CONF_WITH_SIXTOP 1
 
 #if CONTIKI_TARGET_COOJA
diff --git a/tests/13-ieee802154/code/project-tsch-conf.h b/tests/13-ieee802154/code/project-tsch-conf.h
index bbe7c655b..868af4675 100644
--- a/tests/13-ieee802154/code/project-tsch-conf.h
+++ b/tests/13-ieee802154/code/project-tsch-conf.h
@@ -35,21 +35,15 @@
 #if WITH_SECURITY_ON
 #define TEST_CONFIG_TYPE SECURITY_ON
 
-#undef LLSEC802154_CONF_ENABLED
 #define LLSEC802154_CONF_ENABLED 1
 
 #elif WITH_ALL_ENABLED
 #define TEST_CONFIG_TYPE ALL_ENABLED
 
-#undef TSCH_PACKET_CONF_EACK_WITH_DEST_ADDR
 #define TSCH_PACKET_CONF_EACK_WITH_DEST_ADDR 1
-#undef TSCH_PACKET_CONF_EACK_WITH_SRC_ADDR
 #define TSCH_PACKET_CONF_EACK_WITH_SRC_ADDR 1
-#undef TSCH_PACKET_CONF_EB_WITH_TIMESLOT_TIMING
 #define TSCH_PACKET_CONF_EB_WITH_TIMESLOT_TIMING 1
-#undef TSCH_PACKET_CONF_EB_WITH_HOPPING_SEQUENCE
 #define TSCH_PACKET_CONF_EB_WITH_HOPPING_SEQUENCE 1
-#undef TSCH_PACKET_EB_WITH_SLOTFRAME_AND_LINK
 #define TSCH_PACKET_CONF_EB_WITH_SLOTFRAME_AND_LINK 1
 
 #endif
diff --git a/tests/14-rpl-lite/code/project-conf.h b/tests/14-rpl-lite/code/project-conf.h
index f4544bf5e..599ac1cbf 100644
--- a/tests/14-rpl-lite/code/project-conf.h
+++ b/tests/14-rpl-lite/code/project-conf.h
@@ -28,5 +28,4 @@
  */
 #define TCPIP_CONF_ANNOTATE_TRANSMISSIONS 1
 
-#undef RPL_CONF_MOP
 #define RPL_CONF_MOP RPL_MOP_NON_STORING
diff --git a/tests/16-6tisch/code/project-conf.h b/tests/16-6tisch/code/project-conf.h
index 0e857cbd6..3cd35f11d 100644
--- a/tests/16-6tisch/code/project-conf.h
+++ b/tests/16-6tisch/code/project-conf.h
@@ -37,36 +37,27 @@
 //#error "This file is intended to be used for Cooja mote."
 #endif /* CONTIKI_TARGET_COOJA */
 
-#undef SIXTOP_CONF_MAX_SCHEDULING_FUNCTIONS
 #define SIXTOP_CONF_MAX_SCHEDULING_FUNCTIONS 2
 
-#undef SIXTOP_CONF_MAX_TRANSACTIONS
 #define SIXTOP_CONF_MAX_TRANSACTIONS      2
 
-#undef SIXP_CONF_WITH_PAYLOAD_TERMINATION_IE
 #define SIXP_CONF_WITH_PAYLOAD_TERMINATION_IE 1
 
-#undef NBR_TABLE_CONF_MAX_NEIGHBORS
 #define NBR_TABLE_CONF_MAX_NEIGHBORS         2
 
 #define UNIT_TEST_PRINT_FUNCTION test_print_report
 
-#undef TSCH_CONF_WITH_SIXTOP
 #define TSCH_CONF_WITH_SIXTOP 1
 
-#undef TSCH_LOG_CONF_PER_SLOT
 #define TSCH_LOG_CONF_PER_SLOT 1
 
 #define LOG_CONF_LEVEL_6TOP LOG_LEVEL_DBG
 
-#undef TSCH_CONF_AUTOSTART
 #define TSCH_CONF_AUTOSTART 0
 
-#undef IEEE802154_CONF_PANID
 #define IEEE802154_CONF_PANID 0xabcd
 
 /* Custom MAC layer */
-#undef NETSTACK_CONF_MAC
 #define NETSTACK_CONF_MAC        test_mac_driver
 
 #endif /* __PROJECT_CONF_H__ */