diff --git a/src/include/gpxe/resolv.h b/src/include/gpxe/resolv.h
index 772460d9..7c1ee6e2 100644
--- a/src/include/gpxe/resolv.h
+++ b/src/include/gpxe/resolv.h
@@ -158,7 +158,7 @@ extern void resolv_done ( struct resolv_interface *resolv,
 extern void ignore_resolv_done ( struct resolv_interface *resolv,
 			  struct sockaddr *sa, int rc );
 extern struct resolv_interface_operations null_resolv_ops;
-struct resolv_interface null_resolv;
+extern struct resolv_interface null_resolv;
 
 extern int resolv ( struct resolv_interface *resolv, const char *name,
 		    struct sockaddr *sa );