diff --git a/doc/README.x86 b/doc/README.x86
index 7d694b19cc6bdf64f39d559483e97a9ea02acd1b..f28605f200079c3933a9bac8dffaf211113c8386 100644
--- a/doc/README.x86
+++ b/doc/README.x86
@@ -314,6 +314,10 @@ Offset   Description         Controlling config
 
 Overall ROM image size is controlled by CONFIG_ROM_SIZE.
 
+Note that the debug version of the FSP is bigger in size. If this version
+is used, CONFIG_FSP_ADDR needs to be configured to 0xfffb0000 instead of
+the default value 0xfffc0000.
+
 ---
 
 Intel Galileo instructions for bare mode: