diff --git a/module/language/tree-il/peval.scm b/module/language/tree-il/peval.scm
index aadba24a6..4ceb793eb 100644
--- a/module/language/tree-il/peval.scm
+++ b/module/language/tree-il/peval.scm
@@ -527,7 +527,8 @@ top-level bindings from ENV and return the resulting expression."
         (($ <const>) #t)
         (($ <lambda>) #t)
         (($ <lambda-case> _ req opt rest kw inits _ body alternate)
-         (and (every loop inits) (loop body) (loop alternate)))
+         (and (every loop inits) (loop body)
+              (or (not alternate) (loop alternate))))
         (($ <lexical-ref> _ _ gensym)
          (not (assigned-lexical? gensym)))
         (($ <primitive-ref>) #t)