diff --git a/src/Bootstrap4FormServiceProvider.php b/src/Bootstrap4FormServiceProvider.php
index 7f32086..7ee4e2c 100644
--- a/src/Bootstrap4FormServiceProvider.php
+++ b/src/Bootstrap4FormServiceProvider.php
@@ -87,7 +87,12 @@ function (
                 $selected = null,
                 array $selectAttributes = [],
             ): FormGroupBuilder {
-                if (is_null($selected) && in_array('multiple', $selectAttributes)) {
+                if (is_null($selected) &&
+                    (
+                        in_array('multiple', array_values($selectAttributes), true) ||
+                        array_key_exists('multiple', $selectAttributes)
+                    )
+                ) {
                     $selected = Html::value($name) ?? [];
                 }
 
@@ -327,8 +332,7 @@ function (
      */
     public static function addTabIndexIfReadonly(array $attributes): array
     {
-        if (
-            (in_array('readonly', $attributes) || array_key_exists('readonly', $attributes)) &&
+        if ((in_array('readonly', $attributes) || array_key_exists('readonly', $attributes)) &&
             !array_key_exists('tabIndex', $attributes)
         ) {
             $attributes['tabIndex'] = -1;
diff --git a/src/Support/FormGroupBuilder.php b/src/Support/FormGroupBuilder.php
index 8000422..e10561c 100644
--- a/src/Support/FormGroupBuilder.php
+++ b/src/Support/FormGroupBuilder.php
@@ -308,7 +308,9 @@ public function select(
             $selected,
         )->attributes($this->parseInputOptions($selectAttributes)->all());
 
-        if (in_array('multiple', $selectAttributes)) {
+        if (in_array('multiple', array_values($selectAttributes), true) ||
+            array_key_exists('multiple', $selectAttributes)
+        ) {
             $this->input = $this->input->multiple();
         }