diff --git a/src/librustc_mir/interpret/operand.rs b/src/librustc_mir/interpret/operand.rs
index 130343d0b2fb..2fc7d65d655d 100644
--- a/src/librustc_mir/interpret/operand.rs
+++ b/src/librustc_mir/interpret/operand.rs
@@ -512,7 +512,7 @@ pub(super) fn eval_operands(
         };
         // Early-return cases.
         match val.val {
-            ConstValue::Param(_) => return err!(TooGeneric),
+            ConstValue::Param(_) => return err!(TooGeneric), // FIXME(oli-obk): try to monomorphize
             ConstValue::Unevaluated(def_id, substs) => {
                 let instance = self.resolve(def_id, substs)?;
                 return Ok(OpTy::from(self.const_eval_raw(GlobalId {