diff --git a/include/hardware/hwcomposer.h b/include/hardware/hwcomposer.h
index b790fe8..9a7149a 100644
--- a/include/hardware/hwcomposer.h
+++ b/include/hardware/hwcomposer.h
@@ -185,6 +185,10 @@
     HWC_GEOMETRY_CHANGED = 0x00000001,
 };
 
+/*
+ * List of layers.
+ * The handle members of hwLayers elements must be unique.
+ */
 typedef struct hwc_layer_list {
     uint32_t flags;
     size_t numHwLayers;