diff --git a/htdocs/admin/system/dolibarr.php b/htdocs/admin/system/dolibarr.php
index 1dfe1eb03e7..e6c2f1f88f7 100644
--- a/htdocs/admin/system/dolibarr.php
+++ b/htdocs/admin/system/dolibarr.php
@@ -160,11 +160,12 @@ print '<tr '.$bc[$var].'><td width="300">'.$langs->trans("CurrentTimeZone").'</t
 $a=getServerTimeZoneInt('now');
 $b=getServerTimeZoneInt('winter');
 $c=getServerTimeZoneInt('summer');
-$daylight=round($b-$c);
+$daylight=(is_numeric($c) && is_numeric($b))?round($c-$b):'unknown';
+//print $a." ".$b." ".$c." ".$daylight;
 $val=($a>=0?'+':'').$a;
-$val.=' ('.($a>=0?'+':'').($a*3600).')';
+$val.=' ('.($a==='unknown'?'unknown':($a>=0?'+':'').($a*3600)).')';
 $val.=' &nbsp; &nbsp; &nbsp; '.getServerTimeZoneString().' '.($b>=0?'+':'').$b.' ('.($b>=0?'+':'').($b*3600).')';
-$val.=' &nbsp; &nbsp; &nbsp; '.$langs->trans("DaylingSavingTime").': '.yn($daylight);
+$val.=' &nbsp; &nbsp; &nbsp; '.$langs->trans("DaylingSavingTime").': '.($daylight==='unknown'?'unknown':yn($daylight));
 print $form->textwithtooltip($val,$txt,2,1,img_info(''));
 print '</td></tr>'."\n";	// value defined in http://fr3.php.net/manual/en/timezones.europe.php
 $var=!$var;
diff --git a/htdocs/core/lib/date.lib.php b/htdocs/core/lib/date.lib.php
index f7be31e1565..2f5b983c468 100644
--- a/htdocs/core/lib/date.lib.php
+++ b/htdocs/core/lib/date.lib.php
@@ -86,25 +86,39 @@ function getServerTimeZoneInt($refgmtdate='now')
     if (class_exists('DateTime') && ! empty($conf->global->MAIN_NEW_DATE))
     {
         // Method 1 (include daylight)
+        $gmtnow=dol_now('gmt'); $yearref=dol_print_date($gmtnow,'%Y'); $monthref=dol_print_date($gmtnow,'%m'); $dayref=dol_print_date($gmtnow,'%d');
+        if ($refgmtdate == 'now') $newrefgmtdate=$yearref.'-'.$monthref.'-'.$dayref;
+        elseif ($refgmtdate == 'summer') $newrefgmtdate=$yearref.'-05-15';
+        else $newrefgmtdate=$yearref.'-01-01';
         $localtz = new DateTimeZone(getServerTimeZoneString());
-        $localdt = new DateTime($refgmtdate, $localtz);
+        $localdt = new DateTime($newrefgmtdate, $localtz);
         $tmp=-1*$localtz->getOffset($localdt);
+        //print $refgmtdate.'='.$tmp;
     }
     else
     {
         // Method 2 (does not include daylight, not supported by adodb)
         if ($refgmtdate == 'now')
         {
-            $gmtnow=dol_now('gmt');
-            $monthnow=dol_print_date($gmtnow,'%m'); $daynow=dol_print_date($gmtnow,'%d');
+            // We don't know server timezone string, so we don't know location, so we can't guess daylight. We assume we use same than client. Fix is to use MAIN_NEW_DATE.
+            $gmtnow=dol_now('gmt'); $yearref=dol_print_date($gmtnow,'%Y'); $monthref=dol_print_date($gmtnow,'%m'); $dayref=dol_print_date($gmtnow,'%d');
             if (dol_stringtotime($_SESSION['dol_dst_first']) <= $gmtnow && $gmtnow < dol_stringtotime($_SESSION['dol_dst_second'])) $daylight=1;
             else $daylight=0;
-            $tmp=dol_mktime(0,0,0,$monthnow,$daynow,1970,false,0)-dol_mktime(0,0,0,$monthnow,$daynow,1970,true,0)-($daylight*3600);
+            $tmp=dol_mktime(0,0,0,$monthref,$dayref,$yearref,false,0)-dol_mktime(0,0,0,$monthref,$dayref,$yearref,true,0)-($daylight*3600);
+            return 'unknown';
+        }
+        elseif ($refgmtdate == 'summer')
+        {
+            // We don't know server timezone string, so we don't know location, so we can't guess daylight. We assume we use same than client. Fix is to use MAIN_NEW_DATE.
+            $gmtnow=dol_now('gmt'); $yearref=dol_print_date($gmtnow,'%Y'); $monthref='08'; $dayref='01';
+            if (dol_stringtotime($_SESSION['dol_dst_first']) <= dol_stringtotime($yearref.'-'.$monthref.'-'.$dayref) && dol_stringtotime($yearref.'-'.$monthref.'-'.$dayref) < dol_stringtotime($_SESSION['dol_dst_second'])) $daylight=1;
+            else $daylight=0;
+            $tmp=dol_mktime(0,0,0,$monthref,$dayref,$yearref,false,0)-dol_mktime(0,0,0,$monthref,$dayref,$yearref,true,0)-($daylight*3600);
+            return 'unknown';
         }
-        else if ($refgmtdate == 'summer') $tmp=-1;    // TODO
         else $tmp=dol_mktime(0,0,0,1,1,1970);
     }
-    $tz=($tmp<0?1:-1)*abs($tmp/3600);
+    $tz=round(($tmp<0?1:-1)*abs($tmp/3600));
     return $tz;
 }