diff --git a/src/racket/src/schpriv.h b/src/racket/src/schpriv.h
index d77c2c960a..ca0ebbcec3 100644
--- a/src/racket/src/schpriv.h
+++ b/src/racket/src/schpriv.h
@@ -3623,7 +3623,9 @@ typedef struct Scheme_Place {
 
 typedef struct Scheme_Place_Object {
   Scheme_Object so;
+#if defined(MZ_USE_PLACES)
   mzrt_mutex *lock;
+#endif
   char die;
   char pbreak;
   void *signal_handle;