diff --git a/src/librustc_trait_selection/traits/mod.rs b/src/librustc_trait_selection/traits/mod.rs
index b8028a19c8fa5..193ca36e0fd0e 100644
--- a/src/librustc_trait_selection/traits/mod.rs
+++ b/src/librustc_trait_selection/traits/mod.rs
@@ -260,7 +260,7 @@ fn do_normalize_predicates<'tcx>(
             }
         };
         if predicates.needs_infer() {
-            // FIXME: shouldn't we, you know, actually report an error here? or an ICE?
+            tcx.sess.delay_span_bug(span, "encountered inference variables after `fully_resolve`");
             Err(ErrorReported)
         } else {
             Ok(predicates)