diff --git a/src/iso_alloc.c b/src/iso_alloc.c
index 498f2bd..35d9b62 100644
--- a/src/iso_alloc.c
+++ b/src/iso_alloc.c
@@ -813,6 +813,9 @@ INTERNAL_HIDDEN iso_alloc_zone_t *is_zone_usable(iso_alloc_zone_t *zone, size_t
      * chunks smaller than ZONE_1024 */
     if(size > ZONE_1024 && zone->chunk_size >= (size << WASTED_SZ_MULTIPLIER_SHIFT)) {
         return NULL;
+    } 
+    if(size <= ZONE_1024 && zone->chunk_size > ZONE_1024) {
+        return NULL;
     }
 
     if(zone->next_free_bit_slot != BAD_BIT_SLOT) {