diff --git a/admin/inc/class.admin_customfields.inc.php b/admin/inc/class.admin_customfields.inc.php
index 76052ceaa3..2387bb9503 100644
--- a/admin/inc/class.admin_customfields.inc.php
+++ b/admin/inc/class.admin_customfields.inc.php
@@ -279,6 +279,13 @@ class admin_customfields
 		$this->tmpl->exec($exec,$content,$sel_options,$readonlys,$preserve);
 	}
 
+	/**
+	 * Check selectbox values to match regular expression in et2_widget_selectbox.js: _is_multiple_regexp
+	 *
+	 * If values do not match, comma-separated values are not split by comma!
+	 */
+	const CHECK_MULTISELCT_VALUE = '/^[0-9A-Za-z\/_ -]+$/';
+
 	/**
 	 * Edit/Create Custom fields with type
 	 *
@@ -346,6 +353,14 @@ class admin_customfields
 							{
 								list($var_raw,$value) = explode('=',trim($line),2);
 								$var = trim($var_raw);
+								if (!preg_match(self::CHECK_MULTISELCT_VALUE, $var))
+								{
+									Api\Etemplate::set_validation_error('cf_values',
+										lang('Invalide value "%1", use only:', $var)."\n".
+											preg_replace('/^.*\[([^]]+)\].*$/', '$1', self::CHECK_MULTISELCT_VALUE));
+									$action = 'apply';	// do not close the window to show validation error
+									if (!$cf_id) break 2;	// only stop storing of new CFs
+								}
 								$values[$var] = trim($value)==='' ? $var : $value;
 							}
 						}
diff --git a/api/js/etemplate/et2_widget_selectbox.js b/api/js/etemplate/et2_widget_selectbox.js
index 4614f52db9..427eecde88 100644
--- a/api/js/etemplate/et2_widget_selectbox.js
+++ b/api/js/etemplate/et2_widget_selectbox.js
@@ -502,7 +502,7 @@ var et2_selectbox = (function(){ "use strict"; return et2_inputWidget.extend(
 	/**
 	 * Regular expression, to check string-value contains multiple comma-separated values
 	 */
-	_is_multiple_regexp: /^[,0-9A-Za-z/_-]+$/,
+	_is_multiple_regexp: /^[,0-9A-Za-z/_ -]+$/,
 
 	/**
 	 * Regular expression and replace value for escaping values in jQuery selectors used to find options