diff --git a/msvc/h/config.h.msvc6 b/msvc/h/config.h.msvc6
index f7e4905d9..54b30e9db 100644
--- a/msvc/h/config.h.msvc6
+++ b/msvc/h/config.h.msvc6
@@ -30,6 +30,9 @@
 
 /* Userland threads?							*/
 /* #undef ECL_THREADS */
+#ifdef ECL_THREADS
+# define GC_THREADS
+#endif
 
 /* Network streams							*/
 #define TCP 1