diff --git a/phpBB/adm/style/acp_attachments.html b/phpBB/adm/style/acp_attachments.html
index 78d937b967..6448c51c80 100644
--- a/phpBB/adm/style/acp_attachments.html
+++ b/phpBB/adm/style/acp_attachments.html
@@ -208,7 +208,11 @@
 		</dl>
 		<dl>
 			<dt><label for="extgroup_filesize">{L_MAX_EXTGROUP_FILESIZE}{L_COLON}</label></dt>
-			<dd><input type="number" id="extgroup_filesize" min="0" max="999999999999999" step="any" name="max_filesize" value="{EXTGROUP_FILESIZE}" /> <select name="size_select">{S_EXT_GROUP_SIZE_OPTIONS}</select></dd>
+			<dd>
+				<input type="number" id="extgroup_filesize" min="0" max="999999999999999" step="any" name="max_filesize" value="{EXTGROUP_FILESIZE}" />
+				{% from 'form_macros.twig' import select %}
+				{{ select(EXT_GROUP_SIZE_OPTIONS) }}
+			</dd>
 		</dl>
 		<dl>
 			<dt><label for="assigned_extensions">{L_ASSIGNED_EXTENSIONS}{L_COLON}</label></dt>
diff --git a/phpBB/adm/style/form_macros.twig b/phpBB/adm/style/form_macros.twig
index 124f066093..845d039ddd 100644
--- a/phpBB/adm/style/form_macros.twig
+++ b/phpBB/adm/style/form_macros.twig
@@ -8,6 +8,7 @@
 			{% if form_data.maxlength %}maxlength="{{ form_data.maxlength }}"{% endif %}
 			{% if form_data.min %}min="{{ form_data.min }}"{% endif %}
 			{% if form_data.max %}max="{{ form_data.max }}"{% endif %}
+			{% if form_data.step %}step="{{ form_data.step }}"{% endif %}
 			{% if form_data.type == 'password' %}autocomplete="off"{% endif %}
 			{% if form_data.checked %}checked="checked"{% endif %}
 			{% if form_data.class %}class="{{ form_data.class }}"{% endif %}
diff --git a/phpBB/includes/acp/acp_attachments.php b/phpBB/includes/acp/acp_attachments.php
index c03cda951a..329900130e 100644
--- a/phpBB/includes/acp/acp_attachments.php
+++ b/phpBB/includes/acp/acp_attachments.php
@@ -794,7 +794,10 @@ class acp_attachments
 							'ASSIGNED_EXTENSIONS'	=> $assigned_extensions,
 
 							'S_CATEGORY_SELECT'			=> $this->category_select('special_category', $group_id, 'category'),
-							'S_EXT_GROUP_SIZE_OPTIONS'	=> size_select_options($size_format),
+							'EXT_GROUP_SIZE_OPTIONS'	=> [
+								'name'		=> 'size_select',
+								'options'	=> size_select_options($size_format),
+							],
 							'S_EXTENSION_OPTIONS'		=> $s_extension_options,
 							'S_FILENAME_LIST'			=> $filename_list,
 							'S_EDIT_GROUP'				=> true,
@@ -1723,8 +1726,23 @@ class acp_attachments
 		$size_var = $filesize['si_identifier'];
 		$value = $filesize['value'];
 
-		// size and maxlength must not be specified for input of type number
-		return '<input type="number" id="' . $key . '" min="0" max="999999999999999" step="any" name="config[' . $key . ']" value="' . $value . '" /> <select name="' . $key . '">' . size_select_options($size_var) . '</select>';
+		return [
+			[
+				'tag'		=> 'input',
+				'id'		=> $key,
+				'type'		=> 'number',
+				'name'		=> 'config[' . $key . ']',
+				'min'		=> 0,
+				'max'		=> 999999999999999,
+				'step'		=> 'any',
+				'value'		=> $value,
+			],
+			[
+				'tag'		=> 'select',
+				'name'		=> $key,
+				'options'	=> size_select_options($size_var),
+			]
+		];
 	}
 
 	/**
diff --git a/phpBB/includes/functions_admin.php b/phpBB/includes/functions_admin.php
index 621d1a284e..4eaedc4041 100644
--- a/phpBB/includes/functions_admin.php
+++ b/phpBB/includes/functions_admin.php
@@ -160,20 +160,23 @@ function make_forum_select($select_id = false, $ignore_id = false, $ignore_acl =
 */
 function size_select_options($size_compare)
 {
-	global $user;
+	global $language;
 
-	$size_types_text = array($user->lang['BYTES'], $user->lang['KIB'], $user->lang['MIB']);
+	$size_types_text = array($language->lang('BYTES'), $language->lang('KIB'), $language->lang('MIB'));
 	$size_types = array('b', 'kb', 'mb');
 
-	$s_size_options = '';
+	$size_options = [];
 
 	for ($i = 0, $size = count($size_types_text); $i < $size; $i++)
 	{
-		$selected = ($size_compare == $size_types[$i]) ? ' selected="selected"' : '';
-		$s_size_options .= '<option value="' . $size_types[$i] . '"' . $selected . '>' . $size_types_text[$i] . '</option>';
+		$size_options[] = [
+			'value'		=> $size_types[$i],
+			'selected'	=> $size_compare == $size_types[$i],
+			'label'		=> $size_types_text[$i],
+		];
 	}
 
-	return $s_size_options;
+	return $size_options;
 }
 
 /**
diff --git a/phpBB/styles/all/template/macros/form_macros.twig b/phpBB/styles/all/template/macros/form_macros.twig
index 124f066093..845d039ddd 100644
--- a/phpBB/styles/all/template/macros/form_macros.twig
+++ b/phpBB/styles/all/template/macros/form_macros.twig
@@ -8,6 +8,7 @@
 			{% if form_data.maxlength %}maxlength="{{ form_data.maxlength }}"{% endif %}
 			{% if form_data.min %}min="{{ form_data.min }}"{% endif %}
 			{% if form_data.max %}max="{{ form_data.max }}"{% endif %}
+			{% if form_data.step %}step="{{ form_data.step }}"{% endif %}
 			{% if form_data.type == 'password' %}autocomplete="off"{% endif %}
 			{% if form_data.checked %}checked="checked"{% endif %}
 			{% if form_data.class %}class="{{ form_data.class }}"{% endif %}