diff --git a/llvm/include/llvm/ADT/ImmutableSet.h b/llvm/include/llvm/ADT/ImmutableSet.h
--- a/llvm/include/llvm/ADT/ImmutableSet.h
+++ b/llvm/include/llvm/ADT/ImmutableSet.h
@@ -539,7 +539,7 @@
 
   /// add_internal - Creates a new tree that includes the specified
   ///  data and the data from the original tree.  If the original tree
-  ///  already contained the data item, the original tree is returned.
+  ///  already contained the data item, a new tree is returned.
   TreeTy* add_internal(value_type_ref V, TreeTy* T) {
     if (isEmpty(T))
       return createNode(T, V, T);