diff --git a/lib/ParameterParser.php b/lib/ParameterParser.php
index 26b648bb..ad281d70 100644
--- a/lib/ParameterParser.php
+++ b/lib/ParameterParser.php
@@ -91,7 +91,7 @@ class ParameterParser
         $sLangString = $this->getString('accept-language', $sFallback);
 
         if ($sLangString) {
-            if (preg_match_all('/(([a-z]{1,8})(-[a-z]{1,8})?)\s*(;\s*q\s*=\s*(1|0\.[0-9]+))?/i', $sLangString, $aLanguagesParse, PREG_SET_ORDER)) {
+            if (preg_match_all('/(([a-z]{1,8})([-_][a-z]{1,8})?)\s*(;\s*q\s*=\s*(1|0\.[0-9]+))?/i', $sLangString, $aLanguagesParse, PREG_SET_ORDER)) {
                 foreach ($aLanguagesParse as $iLang => $aLanguage) {
                     $aLanguages[$aLanguage[1]] = isset($aLanguage[5])?(float)$aLanguage[5]:1 - ($iLang/100);
                     if (!isset($aLanguages[$aLanguage[2]])) $aLanguages[$aLanguage[2]] = $aLanguages[$aLanguage[1]]/10;
diff --git a/test/php/Nominatim/ParameterParserTest.php b/test/php/Nominatim/ParameterParserTest.php
index 9f51a629..ee2f5e18 100644
--- a/test/php/Nominatim/ParameterParserTest.php
+++ b/test/php/Nominatim/ParameterParserTest.php
@@ -223,5 +223,27 @@ class ParameterParserTest extends \PHPUnit\Framework\TestCase
                            'ref' => 'ref',
                            'type' => 'type',
                           ), $oParams->getPreferredLanguages('default'));
+
+        $oParams = new ParameterParser(array('accept-language' => 'ja_rm,zh_pinyin'));
+        $this->assertSame(array(
+                           'short_name:ja_rm' => 'short_name:ja_rm',
+                           'name:ja_rm' => 'name:ja_rm',
+                           'short_name:zh_pinyin' => 'short_name:zh_pinyin',
+                           'name:zh_pinyin' => 'name:zh_pinyin',
+                           'short_name:ja' => 'short_name:ja',
+                           'name:ja' => 'name:ja',
+                           'short_name:zh' => 'short_name:zh',
+                           'name:zh' => 'name:zh',
+                           'short_name' => 'short_name',
+                           'name' => 'name',
+                           'brand' => 'brand',
+                           'official_name:ja_rm' => 'official_name:ja_rm',
+                           'official_name:zh_pinyin' => 'official_name:zh_pinyin',
+                           'official_name:ja' => 'official_name:ja',
+                           'official_name:zh' => 'official_name:zh',
+                           'official_name' => 'official_name',
+                           'ref' => 'ref',
+                           'type' => 'type',
+                          ), $oParams->getPreferredLanguages('default'));
     }
 }