diff --git a/docs/design/firmware-design.rst b/docs/design/firmware-design.rst
index cae94b5..5fc1335 100644
--- a/docs/design/firmware-design.rst
+++ b/docs/design/firmware-design.rst
@@ -1500,6 +1500,11 @@
 this NOBITS section, making the image unnecessarily bigger. Smaller images
 allow faster loading from the FIP to the main memory.
 
+For BL31, a platform can specify an alternate location for NOBITS sections
+(other than immediately following PROGBITS sections) by setting
+``SEPARATE_NOBITS_REGION`` to 1 and defining ``BL31_NOBITS_BASE`` and
+``BL31_NOBITS_LIMIT``.
+
 Linker scripts and symbols
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