diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 7bf7760..d1bf0d3 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -718,6 +718,10 @@
   CPU. This needs to be enabled only for revisions r0p0, r1p0 and r1p1 of the
   CPU, it is still open.
 
+- ``ERRATA_X3_2742421``: This applies errata 2742421 workaround to
+  Cortex-X3 CPU. This needs to be enabled only for revisions r0p0, r1p0 and
+  r1p1. It is fixed in r1p2.
+
 For Cortex-A510, the following errata build flags are defined :
 
 -  ``ERRATA_A510_1922240``: This applies errata 1922240 workaround to