diff --git a/include/hardware/fb.h b/include/hardware/fb.h
index 135e4aa..9df9416 100644
--- a/include/hardware/fb.h
+++ b/include/hardware/fb.h
@@ -36,6 +36,12 @@
 /*****************************************************************************/
 
 typedef struct framebuffer_device_t {
+    /**
+     * Common methods of the framebuffer device.  This *must* be the first member of
+     * framebuffer_device_t as users of this structure will cast a hw_device_t to
+     * framebuffer_device_t pointer in contexts where it's known the hw_device_t references a
+     * framebuffer_device_t.
+     */
     struct hw_device_t common;
 
     /* flags describing some attributes of the framebuffer */