diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 96a0627c6a4..97c5e4c76da 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -1202,6 +1202,7 @@ pub fn with_caller_bounds(&self,
         }
     }
 
+    /// Construct a parameter environment given an item, impl item, or trait item
     pub fn for_item(cx: &'a TyCtxt<'tcx>, id: NodeId) -> ParameterEnvironment<'a, 'tcx> {
         match cx.map.find(id) {
             Some(ast_map::NodeImplItem(ref impl_item)) => {