diff --git a/docs/plat/arm/arm-build-options.rst b/docs/plat/arm/arm-build-options.rst
index 2aa9738..79b40d1 100644
--- a/docs/plat/arm/arm-build-options.rst
+++ b/docs/plat/arm/arm-build-options.rst
@@ -132,6 +132,12 @@
    valid value greater than 1, the platform code performs required configuration
    to support multi-chip operation.
 
+- ``CSS_SGI_PLATFORM_VARIANT``: Selects the variant of a SGI/RD platform. A
+    particular SGI/RD platform may have multiple variants which may differ in
+    core count, cluster count or other peripherals. This build option is used
+    to select the appropriate platform variant for the build. The range of
+    valid values is platform specific.
+
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