diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 573c63eb6af0..a7163b75d524 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -1938,11 +1938,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         infer::mk_subr(self.infcx(), origin, sub, sup)
     }
 
-    pub fn type_error_message(&self,
-                              sp: Span,
-                              mk_msg: |String| -> String,
-                              actual_ty: Ty<'tcx>,
-                              err: Option<&ty::type_err<'tcx>>) {
+    pub fn type_error_message<M>(&self,
+                                 sp: Span,
+                                 mk_msg: M,
+                                 actual_ty: Ty<'tcx>,
+                                 err: Option<&ty::type_err<'tcx>>) where
+        M: FnOnce(String) -> String,
+    {
         self.infcx().type_error_message(sp, mk_msg, actual_ty, err);
     }
 
diff --git a/src/librustc_typeck/lib.rs b/src/librustc_typeck/lib.rs
index 41ed5b8ec365..0cf43821c82d 100644
--- a/src/librustc_typeck/lib.rs
+++ b/src/librustc_typeck/lib.rs
@@ -74,6 +74,7 @@ This API is completely unstable and subject to change.
 #![feature(default_type_params, globs, import_shadowing, macro_rules, phase, quote)]
 #![feature(slicing_syntax, unsafe_destructor)]
 #![feature(rustc_diagnostic_macros)]
+#![feature(unboxed_closures)]
 #![allow(non_camel_case_types)]
 
 #[phase(plugin, link)] extern crate log;