diff --git a/docs/porting-guide.rst b/docs/porting-guide.rst
index 5cb20fd..671648d 100644
--- a/docs/porting-guide.rst
+++ b/docs/porting-guide.rst
@@ -2454,7 +2454,7 @@
 The value should be obtained from a reliable source of randomness.
 
 This function is only needed if ARMv8.3 pointer authentication is used in the
-Trusted Firmware by building with ``BRANCH_PROTECTION`` option set to non-zero.
+Trusted Firmware by building with ``BRANCH_PROTECTION`` option set to 1, 2 or 3.
 
 Function : plat_get_syscnt_freq2() [mandatory]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~