diff --git a/gc.c b/gc.c
index 28fc26b389..d5b805da71 100644
--- a/gc.c
+++ b/gc.c
@@ -718,6 +718,19 @@ struct heap_page {
 #define GET_HEAP_MARKING_BITS(x)        (&GET_HEAP_PAGE(x)->marking_bits[0])
 #endif
 
+#ifndef ENABLE_VM_OBJSPACE
+# ifdef _WIN32
+/*
+ * TODO: object space independent st_table.
+ * socklist and conlist will be freed exit_handler(), after object
+ * space destruction.
+ */
+#   define ENABLE_VM_OBJSPACE 0
+# else
+#   define ENABLE_VM_OBJSPACE 1
+# endif
+#endif
+
 /* Aliases */
 #if defined(ENABLE_VM_OBJSPACE) && ENABLE_VM_OBJSPACE
 #define rb_objspace (*rb_objspace_of(GET_VM()))
diff --git a/vm_core.h b/vm_core.h
index 4292c8facc..41663fd43e 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -74,19 +74,6 @@
 #include "thread_pthread.h"
 #endif
 
-#ifndef ENABLE_VM_OBJSPACE
-#ifdef _WIN32
-/*
- * TODO: object space independent st_table.
- * socklist and conlist will be freed exit_handler(), after object
- * space destruction.
- */
-#define ENABLE_VM_OBJSPACE 0
-#else
-#define ENABLE_VM_OBJSPACE 1
-#endif
-#endif
-
 #include <setjmp.h>
 #include <signal.h>