diff --git a/cpu/kinetis/Makefile.include b/cpu/kinetis/Makefile.include
index a5f36b4ed0..c2b50b817d 100644
--- a/cpu/kinetis/Makefile.include
+++ b/cpu/kinetis/Makefile.include
@@ -13,7 +13,10 @@ LINKER_SCRIPT = kinetis.ld
 ROM_START_ADDR = 0x00000000
 RAM_BASE_ADDR  = 0x20000000
 RAM_START_ADDR = $$(($(RAM_BASE_ADDR)-($(KINETIS_SRAM_L_SIZE) * 1024)))
-ROM_LEN = $$(($(KINETIS_ROMSIZE) * 1024))
+# Define ROM_LEN with a non arithmetic value as it must be
+# evaluated in `cortexm_common` without a shell context
+# The `K` is correctly handled by both the linker and `cortexm_common`.
+ROM_LEN = $(KINETIS_ROMSIZE)K
 RAM_LEN = $$(($(KINETIS_RAMSIZE) * 1024))
 
 CFLAGS += \