diff --git a/src/kernel/for_each_fn.h b/src/kernel/for_each_fn.h
index 82103c50d..c07205837 100644
--- a/src/kernel/for_each_fn.h
+++ b/src/kernel/for_each_fn.h
@@ -19,7 +19,7 @@ namespace lean {
     The argument \c F must be a lambda (function object) containing the method
 
     <code>
-    void operator()(expr const & e, unsigned offset)
+    bool operator()(expr const & e, unsigned offset)
     </code>
 
     The \c offset is the number of binders under which \c e occurs.