diff --git a/cpu/lpc1768/Makefile.features b/cpu/lpc1768/Makefile.features
index 01cd4811b7..1c25c072c7 100644
--- a/cpu/lpc1768/Makefile.features
+++ b/cpu/lpc1768/Makefile.features
@@ -1,3 +1,5 @@
+# This CPU only implements one CPU_MODEL with the same name
+CPU_MODEL = lpc1768
 FEATURES_PROVIDED += periph_cpuid
 FEATURES_PROVIDED += periph_pm
 
diff --git a/makefiles/arch/cortexm.inc.mk b/makefiles/arch/cortexm.inc.mk
index 895342d4ae..57f22b9d60 100644
--- a/makefiles/arch/cortexm.inc.mk
+++ b/makefiles/arch/cortexm.inc.mk
@@ -1,3 +1,7 @@
+ifeq (,$(CPU_MODEL))
+  $(error CPU_MODEL must have been defined by the board/cpu Makefile.features)
+endif
+
 # Target triple for the build. Use arm-none-eabi if you are unsure.
 export TARGET_ARCH ?= arm-none-eabi
 
@@ -39,9 +43,6 @@ export USEMODULE += cortexm_common_periph
 # all cortex MCU's use newlib as libc
 export USEMODULE += newlib
 
-# set default for CPU_MODEL
-export CPU_MODEL ?= $(CPU)
-
 
 # extract version inside the first parentheses
 ARM_GCC_VERSION = $(shell $(TARGET_ARCH)-gcc --version | sed -n '1 s/[^(]*(\([^\)]*\)).*/\1/p')