diff --git a/racket/src/racket/win_tls.inc b/racket/src/racket/win_tls.inc
index fdfc3376bb..deace2adcb 100644
--- a/racket/src/racket/win_tls.inc
+++ b/racket/src/racket/win_tls.inc
@@ -1,33 +1,39 @@
 #ifdef IMPLEMENT_THREAD_LOCAL_VIA_WIN_TLS
+
+# ifndef NO_TLS_INDEX_FOR_WIN_TLS
 extern intptr_t _tls_index;
+#  define REGISTER_TLS_INDEX_ARG _tls_index
+# else
+#  define REGISTER_TLS_INDEX_ARG 0
+# endif
+
 # ifdef __MINGW32__
 static __thread void *tls_space;
 # else
 static __declspec(thread) void *tls_space;
 # endif
-#endif
 
-# ifdef IMPLEMENT_THREAD_LOCAL_VIA_WIN_TLS
 static void register_win_tls()
 {
-#  ifdef __MINGW32__
+# ifdef __MINGW32__
   {
     /* gcc declares space for the thread-local variable in a way that
        the OS can set up, but its doesn't actually map variables
        through the OS-supplied mechanism. Just assume that the first
        thread-local variable is ours. */
     void **base;
-#  ifdef _WIN64
+# ifdef _WIN64
     asm("mov %%gs:(0x58), %0;" :"=r"(base));
-#  else
-    asm("mov %%fs:(0x2C), %0;" :"=r"(base));
-#  endif
-    scheme_register_tls_space(*base, _tls_index);
-  }
-#  else
-  scheme_register_tls_space(&tls_space, _tls_index);
-#  endif
-}
 # else
-static void register_win_tls() {}
+    asm("mov %%fs:(0x2C), %0;" :"=r"(base));
 # endif
+    scheme_register_tls_space(*base, REGISTER_TLS_INDEX_ARG);
+  }
+# else
+  scheme_register_tls_space(&tls_space, REGISTER_TLS_INDEX_ARG);
+# endif
+}
+
+#else
+static void register_win_tls() {}
+#endif