diff --git a/src/racket/src/thread.c b/src/racket/src/thread.c
index 9ae3800b4a..ed3761ab6e 100644
--- a/src/racket/src/thread.c
+++ b/src/racket/src/thread.c
@@ -191,6 +191,8 @@ THREAD_LOCAL_DECL(static Scheme_Custodian *last_custodian);
 THREAD_LOCAL_DECL(static Scheme_Hash_Table *limited_custodians = NULL);
 READ_ONLY static Scheme_Object *initial_inspector;
 
+THREAD_LOCAL_DECL(Scheme_Config *initial_config);
+
 #ifndef MZ_PRECISE_GC
 static int cust_box_count, cust_box_alloc;
 static Scheme_Custodian_Box **cust_boxes;