diff --git a/mod/photos.php b/mod/photos.php
index 4bca8275e3..d44afa588c 100644
--- a/mod/photos.php
+++ b/mod/photos.php
@@ -916,13 +916,14 @@ function photos_content(App $a)
 
 		$maximagesize_Mbytes = 0;
 		// Get the relevant size limits for uploads. Abbreviated var names: MaxImageSize -> mis; upload_max_filesize -> umf
-		$mis_bytes = DI::config()->get('system', 'maximagesize');
+		$mis_bytes = Strings::getBytesFromShorthand(DI::config()->get('system', 'maximagesize'));
 		$umf_bytes = Strings::getBytesFromShorthand(ini_get('upload_max_filesize'));
 
 		// When PHP is configured with upload_max_filesize less than maximagesize provide this lower limit.
 		$maximagesize_Mbytes = (is_numeric($mis_bytes) && ($mis_bytes < $umf_bytes) ? $mis_bytes : $umf_bytes) / (1048576);
 
-		$usage_message = DI::l10n()->t('The maximum accepted image size is %.3g MB', $maximagesize_Mbytes);
+		// @todo We may be want to use appropriate binary prefixed dynamicly
+		$usage_message = DI::l10n()->t('The maximum accepted image size is %.6g MB', $maximagesize_Mbytes);
 
 		$tpl = Renderer::getMarkupTemplate('photos_upload.tpl');
 
diff --git a/src/Module/Admin/Site.php b/src/Module/Admin/Site.php
index a6931ce916..8aa43c5564 100644
--- a/src/Module/Admin/Site.php
+++ b/src/Module/Admin/Site.php
@@ -34,6 +34,7 @@ use Friendica\Model\User;
 use Friendica\Module\BaseAdmin;
 use Friendica\Module\Conversation\Community;
 use Friendica\Module\Register;
+use Friendica\Navigation\SystemMessages;
 use Friendica\Protocol\Relay;
 use Friendica\Util\BasePath;
 use Friendica\Util\EMailer\MailBuilder;
@@ -41,6 +42,8 @@ use Friendica\Util\Strings;
 
 class Site extends BaseAdmin
 {
+//	const SHORTHAND_REGEX = '/*/i';
+
 	protected function post(array $request = [])
 	{
 		self::checkAdminAccess();
@@ -68,7 +71,7 @@ class Site extends BaseAdmin
 		$language         = (!empty($_POST['language'])         ? trim($_POST['language'])      : '');
 		$theme            = (!empty($_POST['theme'])            ? trim($_POST['theme'])         : '');
 		$theme_mobile     = (!empty($_POST['theme_mobile'])     ? trim($_POST['theme_mobile'])  : '');
-		$maximagesize     = (!empty($_POST['maximagesize'])     ? intval(trim($_POST['maximagesize']))               : 0);
+		$maximagesize     = (!empty($_POST['maximagesize'])     ? trim($_POST['maximagesize'])              : 0);
 		$maximagelength   = (!empty($_POST['maximagelength'])   ? intval(trim($_POST['maximagelength']))             : -1);
 		$jpegimagequality = (!empty($_POST['jpegimagequality']) ? intval(trim($_POST['jpegimagequality']))           : 100);
 
@@ -240,7 +243,11 @@ class Site extends BaseAdmin
 		} else {
 			DI::config()->set('system', 'singleuser', $singleuser);
 		}
-		DI::config()->set('system', 'maximagesize'           , $maximagesize);
+		if (preg_match('/\d+(?:\s*[kmg])?/i', $maximagesize)) {
+			DI::config()->set('system', 'maximagesize', $maximagesize);
+		} else {
+			DI::sysmsg()->addNotice(DI::l10n()->t('%s is no valid input for maximum image size', $maximagesize));
+		}
 		DI::config()->set('system', 'max_image_length'       , $maximagelength);
 		DI::config()->set('system', 'jpeg_quality'           , $jpegimagequality);
 
@@ -471,7 +478,7 @@ class Site extends BaseAdmin
 			'$maximagesize'     => ['maximagesize', DI::l10n()->t('Maximum image size'), DI::config()->get('system', 'maximagesize'), DI::l10n()->t('Maximum size in bytes of uploaded images. Default is 0, which means no limits.
 													The value of <code>upload_max_filesize</code> in your <code>PHP.ini</code> needs be set to at least the desired limit.
 													Currently <code>upload_max_filesize</code> is set to %s (%sB)', Strings::getBytesFromShorthand(ini_get('upload_max_filesize')), ini_get('upload_max_filesize')),
-													'1 kB = 1 KiB = 1024 Bytes'],
+													'', '', '', '\d+(?:\s*[kmg])?'],
 			'$maximagelength'   => ['maximagelength', DI::l10n()->t('Maximum image length'), DI::config()->get('system', 'max_image_length'), DI::l10n()->t('Maximum length in pixels of the longest side of uploaded images. Default is -1, which means no limits.')],
 			'$jpegimagequality' => ['jpegimagequality', DI::l10n()->t('JPEG image quality'), DI::config()->get('system', 'jpeg_quality'), DI::l10n()->t('Uploaded JPEGS will be saved at this quality setting [0-100]. Default is 100, which is full quality.')],
 
diff --git a/view/templates/field_input.tpl b/view/templates/field_input.tpl
index 3455891b9d..95a13cfb7b 100644
--- a/view/templates/field_input.tpl
+++ b/view/templates/field_input.tpl
@@ -1,7 +1,7 @@
 	
 	<div class="field input" id="wrapper_{{$field.0}}">
 		<label for="id_{{$field.0}}">{{$field.1}}{{if $field.4}} <span class="required" title="{{$field.4}}">*</span>{{/if}}</label>
-		<input type="{{$field.6|default:'text'}}" name="{{$field.0}}" id="id_{{$field.0}}" value="{{$field.2}}"{{if $field.4}} required{{/if}}{{if $field.5 eq "autofocus"}} autofocus{{elseif $field.5}} {{$field.5 nofilter}}{{/if}} aria-describedby="{{$field.0}}_tip" dir="auto">
+		<input type="{{$field.6|default:'text'}}" pattern="{{$field.7}}"  name="{{$field.0}}" id="id_{{$field.0}}" value="{{$field.2}}"{{if $field.4}} required{{/if}}{{if $field.5 eq "autofocus"}} autofocus{{elseif $field.5}} {{$field.5 nofilter}}{{/if}} aria-describedby="{{$field.0}}_tip" dir="auto">
 	{{if $field.3}}
 		<span class="field_help" role="tooltip" id="{{$field.0}}_tip">{{$field.3 nofilter}}</span>
 	{{/if}}
diff --git a/view/theme/frio/css/mod_admin.css b/view/theme/frio/css/mod_admin.css
index 3475d1d82a..355cfd1401 100644
--- a/view/theme/frio/css/mod_admin.css
+++ b/view/theme/frio/css/mod_admin.css
@@ -40,3 +40,11 @@ tr.details th {
 .adminpage td {
 	word-break: break-all;
 }
+
+.adminpage input[id=id_maximagesize]:valid {
+	background-color: palegreen;
+}
+
+.adminpage input[id=id_maximagesize]:invalid {
+	background-color: lightpink;
+}
\ No newline at end of file
diff --git a/view/theme/frio/templates/field_input.tpl b/view/theme/frio/templates/field_input.tpl
index 3a9e54d06a..9812e3466f 100644
--- a/view/theme/frio/templates/field_input.tpl
+++ b/view/theme/frio/templates/field_input.tpl
@@ -3,7 +3,7 @@
 	{{if !isset($label) || $label != false }}
 		<label for="id_{{$field.0}}" id="label_{{$field.0}}">{{$field.1 nofilter}}{{if $field.4}} <span class="required" title="{{$field.4}}">*</span>{{/if}}</label>
 	{{/if}}
-		<input class="form-control" name="{{$field.0}}" id="id_{{$field.0}}" type="{{$field.6|default:'text'}}" value="{{$field.2}}"{{if $field.4}} required{{/if}}{{if $field.5 eq "autofocus"}} autofocus{{elseif $field.5}} {{$field.5 nofilter}}{{/if}} aria-describedby="{{$field.0}}_tip">
+		<input class="form-control" name="{{$field.0}}" id="id_{{$field.0}}" type="{{$field.6|default:'text'}}" {{if $field.7}}pattern="{{$field.7}}"{{/if}} value="{{$field.2}}"{{if $field.4}} required{{/if}}{{if $field.5 eq "autofocus"}} autofocus{{elseif $field.5}} {{$field.5 nofilter}}{{/if}} aria-describedby="{{$field.0}}_tip">
 	{{if $field.3}}
 		<span class="help-block" id="{{$field.0}}_tip" role="tooltip">{{$field.3 nofilter}}</span>
 	{{/if}}