diff --git a/Core.Arango.DevExtreme/ArangoTransform.cs b/Core.Arango.DevExtreme/ArangoTransform.cs
index a54c105..d8bee5a 100644
--- a/Core.Arango.DevExtreme/ArangoTransform.cs
+++ b/Core.Arango.DevExtreme/ArangoTransform.cs
@@ -868,7 +868,7 @@ public List<DxGroupResult> BuildGrouping(ArangoTransform aq, List<JObject> list,
 
             var key = aq.Groups[level];
 
-            var items = list.GroupBy(x => x.Value<string>(key)).ToList();
+            var items = list.GroupBy(x => x.Value<object>(key)).ToList();
 
             foreach (var item in items)
             {
diff --git a/Core.Arango.DevExtreme/DxGroupResult.cs b/Core.Arango.DevExtreme/DxGroupResult.cs
index 2b610c6..2222d4b 100644
--- a/Core.Arango.DevExtreme/DxGroupResult.cs
+++ b/Core.Arango.DevExtreme/DxGroupResult.cs
@@ -8,7 +8,7 @@ public class DxGroupResult
     {
         [JsonProperty("key")] 
         [JsonPropertyName("key")]
-        public string Key { get; set; }
+        public object Key { get; set; }
 
         [JsonProperty("display", NullValueHandling = NullValueHandling.Ignore)]
         [JsonPropertyName("display")]