diff --git a/src/kernel/environment.cpp b/src/kernel/environment.cpp
index a1691cb1d..06c7c4c03 100644
--- a/src/kernel/environment.cpp
+++ b/src/kernel/environment.cpp
@@ -16,7 +16,7 @@ namespace lean {
 */
 class noop_normalizer_extension : public normalizer_extension {
 public:
-    virtual optional<expr> operator()(expr const &, extension_context const &) const {
+    virtual optional<expr> operator()(expr const &, extension_context &) const {
         return none_expr();
     }
 };
diff --git a/src/kernel/environment.h b/src/kernel/environment.h
index fcc7a102e..0a83e3229 100644
--- a/src/kernel/environment.h
+++ b/src/kernel/environment.h
@@ -31,7 +31,7 @@ class certified_definition;
 class normalizer_extension {
 public:
     virtual ~normalizer_extension() {}
-    virtual optional<expr> operator()(expr const & e, extension_context const & ctx) const = 0;
+    virtual optional<expr> operator()(expr const & e, extension_context & ctx) const = 0;
 };
 
 /**