diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index d03daf8..8743b04 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -759,6 +759,10 @@
   Cortex-X3 CPU. This needs to be enabled only for revisions r0p0, r1p0 and
   r1p1. It is fixed in r1p2.
 
+- ``ERRATA_X3_2779509``: This applies errata 2779509 workaround to Cortex-X3
+  CPU. This needs to be enabled only for revisions r0p0, r1p0 and r1p1 of the
+  CPU. It is fixed in r1p2.
+
 For Cortex-A510, the following errata build flags are defined :
 
 -  ``ERRATA_A510_1922240``: This applies errata 1922240 workaround to