diff --git a/libguile/gc.c b/libguile/gc.c
index 4808625cf..de1b3ee0d 100644
--- a/libguile/gc.c
+++ b/libguile/gc.c
@@ -54,7 +54,7 @@
 
 #ifdef __ia64__
 #include <ucontext.h>
-extern unsigned long __libc_ia64_register_backing_store_base;
+extern unsigned long * __libc_ia64_register_backing_store_base;
 #endif
 
 #include "libguile/_scm.h"