diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 380f5a586655..41db7c5f0390 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -1373,7 +1373,7 @@ impl<'tcx> Predicate<'tcx> {
             }
         };
 
-        // The only reason to collect into a vector here is that I was
+        // FIXME: The only reason to collect into a vector here is that I was
         // too lazy to make the full (somewhat complicated) iterator
         // type that would be needed here. But I wanted this fn to
         // return an iterator conceptually, rather than a `Vec`, so as