diff --git a/sys/riotboot/Makefile.include b/sys/riotboot/Makefile.include
index 4e2d9b6c62..56e5aa9952 100644
--- a/sys/riotboot/Makefile.include
+++ b/sys/riotboot/Makefile.include
@@ -1,6 +1,8 @@
-# Indicate the reserved space for a header, 256B by default
-# Notice that it must be 256B aligned. This is restricted by
-# the Cortex-M0+/3/4/7 architecture
+# Indicate the reserved space for a header, 256B by default.
+# The value must respect the cpu alignment requirements for the specific
+# cpu, it can be re-defined in the cpu Makefile.include accordingly.
+# e.g: `cortex-m` vector-table comes after `riotboot_hdr` and must be naturally
+# aligned according to CPU_IRQ_NUMOF (ref: cpu/cortexm_common/Makefile.include)
 RIOTBOOT_HDR_LEN ?= 0x100
 
 # By default, slot 0 is found just after RIOTBOOT_LEN. Slot 1 after