diff --git a/base-nova/include/nova/syscall-generic.h b/base-nova/include/nova/syscall-generic.h
index 52b2645f9..8eefef099 100644
--- a/base-nova/include/nova/syscall-generic.h
+++ b/base-nova/include/nova/syscall-generic.h
@@ -403,7 +403,8 @@ namespace Nova {
 		 *
 		 * \param exception  true to append the item to an exception reply
 		 */
-		void append_item(Crd crd, mword_t sel_hotspot,
+		__attribute__((warn_unused_result))
+		bool append_item(Crd crd, mword_t sel_hotspot,
 		                 bool kern_pd = false,
 		                 bool update_guest_pt = false)
 		{
@@ -411,6 +412,12 @@ namespace Nova {
 			items += 1 << 16;
 			Item *item = reinterpret_cast<Item *>(this) + (PAGE_SIZE_BYTE / sizeof(struct Item)) - (items >> 16);
 
+			/* check that there is enough space left on UTCB */
+			if (msg + msg_words() >= reinterpret_cast<mword_t *>(item)) {
+				items -= 1 << 16;
+				return false;
+			}
+
 			/* map from hypervisor or current pd */
 			unsigned h = kern_pd ? (1 << 11) : 0;
 
@@ -420,6 +427,7 @@ namespace Nova {
 			item->hotspot = crd.hotspot(sel_hotspot) | g | h | 1;
 			item->crd = crd.value();
 
+			return true;
 		}
 
 		mword_t mtd_value() const { return static_cast<Mtd>(mtd).value(); }