diff --git a/src/Aggregation/HistogramAggregation.php b/src/Aggregation/HistogramAggregation.php
index 3c5aaca426552dc0156a33fdcab1bb0c89349da3..1d4bbbe68d0218c2900c69ad491d66a574b5130d 100644
--- a/src/Aggregation/HistogramAggregation.php
+++ b/src/Aggregation/HistogramAggregation.php
@@ -122,7 +122,11 @@ class HistogramAggregation extends AbstractAggregation
      */
     public function getOrder()
     {
-        return [$this->orderMode => $this->orderDirection];
+        if ($this->orderMode && $this->orderDirection) {
+            return [$this->orderMode => $this->orderDirection];
+        } else {
+            return null;
+        }
     }
 
     /**