diff --git a/src/mzscheme/src/eval.c b/src/mzscheme/src/eval.c
index c6ac8e9eb0..a4a7aa0fa6 100644
--- a/src/mzscheme/src/eval.c
+++ b/src/mzscheme/src/eval.c
@@ -1085,7 +1085,7 @@ static Scheme_Object *try_apply(Scheme_Object *f, Scheme_Object *args, Scheme_Ob
   Scheme_Object * volatile result;
   mz_jmp_buf *savebuf, newbuf;
 
-  scheme_current_thread->constant_folding = context;
+  scheme_current_thread->constant_folding = (context ? context : scheme_true);
   savebuf = scheme_current_thread->error_buf;
   scheme_current_thread->error_buf = &newbuf;