diff --git a/src/frontends/lean/elaborator.cpp b/src/frontends/lean/elaborator.cpp
index 090520735d..5392e6547a 100644
--- a/src/frontends/lean/elaborator.cpp
+++ b/src/frontends/lean/elaborator.cpp
@@ -98,7 +98,7 @@ class elaborator {
         }
     };
 
-    lazy_list<a_choice> choose(std::shared_ptr<choice_elaborator> const & c) {
+    lazy_list<a_choice> choose(std::shared_ptr<choice_elaborator> c) {
         return mk_lazy_list<a_choice>([=]() {
                 auto s = c->next();
                 if (s)
diff --git a/src/library/unifier.cpp b/src/library/unifier.cpp
index 08ae19db01..1b046a8354 100644
--- a/src/library/unifier.cpp
+++ b/src/library/unifier.cpp
@@ -1027,7 +1027,7 @@ struct unifier_fn {
     }
 };
 
-lazy_list<substitution> unify(std::shared_ptr<unifier_fn> const & u) {
+lazy_list<substitution> unify(std::shared_ptr<unifier_fn> u) {
     return mk_lazy_list<substitution>([=]() {
             auto s = u->next();
             if (s)