diff --git a/README.md b/README.md
index 9c61e195..9828c113 100644
--- a/README.md
+++ b/README.md
@@ -49,6 +49,8 @@ Change directory to `build` then run `ccmake` to create Makefile. Once `Makefile
 
 Actually you don't necessarily need to move to `build` directory before running `ccmake` (in that case `$ ccmake .`), but I strongly recommend to follow above instruction.
     
+Before generating Makefile, you can change some compilation switches to enable or disable optional features. Take *NAN_BOXING* for example, when you turn on "Use C11 feature" flag and the platform supports addresses of 48bit length, it is enabled.
+
 ### Build
 
 A built executable binary will be under bin/ directory and shared libraries under lib/.
diff --git a/docs/deploy.rst b/docs/deploy.rst
index 2268ad01..3c8b9ceb 100644
--- a/docs/deploy.rst
+++ b/docs/deploy.rst
@@ -25,6 +25,8 @@ Change directory to `build` then run `ccmake` to create Makefile. Once `Makefile
 
 Actually you don't necessarily need to move to `build` directory before running `ccmake` (in that case `$ ccmake .`), but I strongly recommend to follow above instruction.
 
+Before generating Makefile, you can change some compilation switches to enable or disable optional features. Take *NAN_BOXING* for example, when you turn on "Use C11 feature" flag and the platform supports addresses of 48bit length, it is enabled.
+
 Build
 ^^^^^