diff --git a/src/Eloquent/Builder.php b/src/Eloquent/Builder.php
index b629dc7f6..e89c0800d 100644
--- a/src/Eloquent/Builder.php
+++ b/src/Eloquent/Builder.php
@@ -309,7 +309,7 @@ public function eagerLoadRelations(array $models)
                         ->where($withAggregate['constraints'])
                         ->whereIn($withAggregate['relation']->getForeignKeyName(), $modelIds)
                         ->groupBy($withAggregate['relation']->getForeignKeyName())
-                        ->aggregate($withAggregate['function'], $withAggregate['column'] ?? [$withAggregate['relation']->getPrimaryKeyName()]);
+                        ->aggregate($withAggregate['function'], [$withAggregate['column']]);
 
                     foreach ($models as $model) {
                         $value = $withAggregate['function'] === 'count' ? 0 : null;
diff --git a/src/Query/Builder.php b/src/Query/Builder.php
index 3998bb65e..cfd2907ae 100644
--- a/src/Query/Builder.php
+++ b/src/Query/Builder.php
@@ -28,6 +28,7 @@
 use Override;
 use RuntimeException;
 use stdClass;
+use TypeError;
 
 use function array_fill_keys;
 use function array_is_list;
@@ -335,7 +336,7 @@ public function toMql(): array
             if ($this->aggregate) {
                 $function = $this->aggregate['function'];
 
-                foreach ((array) $this->aggregate['columns'] as $column) {
+                foreach ($this->aggregate['columns'] as $column) {
                     // Add unwind if a subdocument array should be aggregated
                     // column: subarray.price => {$unwind: '$subarray'}
                     $splitColumns = explode('.*.', $column);
@@ -344,7 +345,7 @@ public function toMql(): array
                         $column    = implode('.', $splitColumns);
                     }
 
-                    $aggregations = blank($this->aggregate['columns']) ? [] : (array) $this->aggregate['columns'];
+                    $aggregations = blank($this->aggregate['columns']) ? [] : $this->aggregate['columns'];
 
                     if (in_array('*', $aggregations) && $function === 'count' && empty($group['_id'])) {
                         $options = $this->inheritConnectionOptions($this->options);
@@ -484,11 +485,11 @@ public function getFresh($columns = [], $returnLazy = false)
         // here to either the passed columns, or the standard default of retrieving
         // all of the columns on the table using the "wildcard" column character.
         if ($this->columns === null) {
-            $this->columns = (array) $columns;
+            $this->columns = $columns;
         }
 
         // Drop all columns if * is present, MongoDB does not work this way.
-        if (in_array('*', (array) $this->columns)) {
+        if (in_array('*', $this->columns)) {
             $this->columns = [];
         }
 
@@ -556,6 +557,8 @@ public function generateCacheKey()
     /** @return ($function is null ? AggregationBuilder : mixed) */
     public function aggregate($function = null, $columns = ['*'])
     {
+        assert(is_array($columns), new TypeError(sprintf('Argument #2 ($columns) must be of type array, %s given', get_debug_type($columns))));
+
         if ($function === null) {
             if (! trait_exists(FluentFactoryTrait::class)) {
                 // This error will be unreachable when the mongodb/builder package will be merged into mongodb/mongodb