diff --git a/src/Actions/ExportToExcel.php b/src/Actions/ExportToExcel.php
index fde8e60..7668ae5 100644
--- a/src/Actions/ExportToExcel.php
+++ b/src/Actions/ExportToExcel.php
@@ -193,7 +193,7 @@ public function map($row): array
             $row->setHidden([]);
             $row = $this->replaceFieldValuesWhenOnResource(
                 $row,
-                is_array($only) ? $only : array_keys($row->attributesToArray())
+                $only
             );
         }
 
diff --git a/src/Concerns/Only.php b/src/Concerns/Only.php
index 4ffd260..985acfd 100644
--- a/src/Concerns/Only.php
+++ b/src/Concerns/Only.php
@@ -8,9 +8,9 @@
 trait Only
 {
     /**
-     * @var array|null
+     * @var array
      */
-    protected $only;
+    protected $only = [];
 
     /**
      * @var bool
@@ -50,7 +50,7 @@ public function allFields()
     }
 
     /**
-     * @return array|null
+     * @return array
      */
     public function getOnly()
     {
@@ -64,8 +64,14 @@ protected function handleOnly(ExportActionRequest $request)
     {
         // If not a specific only array, and user wants only index fields,
         // fill the only with the index fields.
-        if ($this->onlyIndexFields && (!is_array($this->only) || count($this->only) === 0)) {
-            $this->only = $request->indexFields($request->newResource());
+        $indexFields = $request->indexFields($request->newResource());
+
+        if ($this->onlyIndexFields && count($this->only) === 0) {
+            $this->only = $indexFields;
+        } elseif (!$this->onlyIndexFields) {
+            $modelAttributes = optional($request->toQuery()->first())->attributesToArray() ?: [];
+
+            $this->only = array_merge(array_keys($modelAttributes), $indexFields);
         }
     }
 }