diff --git a/board/sandbox/README.sandbox b/board/sandbox/README.sandbox
index 48c1e2b..5e8fa58b 100644
--- a/board/sandbox/README.sandbox
+++ b/board/sandbox/README.sandbox
@@ -435,6 +435,13 @@
 This approach can be used on normal boards as well as sandbox.
 
 
+SDL_CONFIG
+----------
+
+If sdl-config is on a different path from the default, set the SDL_CONFIG
+environment variable to the correct pathname before building U-Boot.
+
+
 Testing
 -------