diff --git a/sandbox/vm/cache.c b/sandbox/vm/cache.c
index 1efa96c..a303952 100644
--- a/sandbox/vm/cache.c
+++ b/sandbox/vm/cache.c
@@ -143,9 +143,13 @@ void *vm_cache_alloc(vm_cache_t *cache, vm_flags_t flags)
 	vm_slab_t *slab = NULL;
 	if (!queue_empty(&cache->c_slabs_partial)) {
 		/* prefer using up partially-full slabs before taking a fresh one */
-		slab = QUEUE_CONTAINER(vm_slab_t, s_list, queue_pop_front(&cache->c_slabs_partial));
+		queue_entry_t *slab_entry = queue_pop_front(&cache->c_slabs_partial);
+		assert(slab_entry);
+		slab = QUEUE_CONTAINER(vm_slab_t, s_list, slab_entry);
 	} else if (!queue_empty(&cache->c_slabs_empty)) {
-		slab = QUEUE_CONTAINER(vm_slab_t, s_list, queue_pop_front(&cache->c_slabs_empty));
+		queue_entry_t *slab_entry = queue_pop_front(&cache->c_slabs_empty);
+		assert(slab_entry);
+		slab = QUEUE_CONTAINER(vm_slab_t, s_list, slab_entry);
 	} else {
 		/* we've run out of slabs. create a new one */
 		slab = alloc_slab(cache, flags);