diff --git a/src/kernel_services/ast_queries/cil.mli b/src/kernel_services/ast_queries/cil.mli
index 5bdb0939b7a617338d8b221ca8cffe24fad7c7a3..df4e0e12389593b8b0423c1bf6d46e91dd878bc5 100644
--- a/src/kernel_services/ast_queries/cil.mli
+++ b/src/kernel_services/ast_queries/cil.mli
@@ -1223,7 +1223,7 @@ val partitionAttributes:  default:attributeClass ->
                 attribute list   (* AttrType *)
 
 (** Add an attribute. Maintains the attributes in sorted order of the second
-    argument *)
+    argument. The attribute is not added if it is already there. *)
 val addAttribute: attribute -> attributes -> attributes
 
 (** Add a list of attributes. Maintains the attributes in sorted order. The