diff --git a/examples/gnrc_networking/Makefile b/examples/gnrc_networking/Makefile
index 7aac1aee1282c914dfe5e460be45a466d267c051..b8b53ac282c26e4163bbaee83e8644219d9aeaca 100644
--- a/examples/gnrc_networking/Makefile
+++ b/examples/gnrc_networking/Makefile
@@ -67,7 +67,7 @@ ifneq (,$(filter cc110x,$(USEMODULE)))          # radio is cc110x sub-GHz
 else
   ifneq (,$(filter at86rf212b,$(USEMODULE)))    # radio is IEEE 802.15.4 sub-GHz
     DEFAULT_CHANNEL ?= 5
-    FLAGS += -DIEEE802154_DEFAULT_SUBGHZ_CHANNEL=$(DEFAULT_CHANNEL)
+    CFLAGS += -DIEEE802154_DEFAULT_SUBGHZ_CHANNEL=$(DEFAULT_CHANNEL)
   else                                          # radio is IEEE 802.15.4 2.4 GHz
     DEFAULT_CHANNEL ?= 26
     CFLAGS += -DIEEE802154_DEFAULT_CHANNEL=$(DEFAULT_CHANNEL)
diff --git a/tests/gnrc_udp/Makefile b/tests/gnrc_udp/Makefile
index f5bad0c7c8219fbcd35920269f7fda482fb6a892..91919599c363a98fb721cae2770cea5039cb68a3 100644
--- a/tests/gnrc_udp/Makefile
+++ b/tests/gnrc_udp/Makefile
@@ -31,7 +31,7 @@ ifneq (,$(filter cc110x,$(USEMODULE)))          # radio is cc110x sub-GHz
 else
   ifneq (,$(filter at86rf212b,$(USEMODULE)))    # radio is IEEE 802.15.4 sub-GHz
     DEFAULT_CHANNEL ?= 5
-    FLAGS += -DIEEE802154_DEFAULT_SUBGHZ_CHANNEL=$(DEFAULT_CHANNEL)
+    CFLAGS += -DIEEE802154_DEFAULT_SUBGHZ_CHANNEL=$(DEFAULT_CHANNEL)
   else                                          # radio is IEEE 802.15.4 2.4 GHz
     DEFAULT_CHANNEL ?= 26
     CFLAGS += -DIEEE802154_DEFAULT_CHANNEL=$(DEFAULT_CHANNEL)