diff --git a/xlsxwriter.class.php b/xlsxwriter.class.php
index 118341843..93be5cd60 100644
--- a/xlsxwriter.class.php
+++ b/xlsxwriter.class.php
@@ -302,15 +302,12 @@ protected function writeCell(XLSXWriter_BuffererWriter &$file, $row_number, $col
 			$file->write('<c r="'.$cell_name.'" s="'.$cell_style_idx.'" t="n"><v>'.self::xmlspecialchars($value).'</v></c>');//int,float,currency
 		} elseif ($num_format_type=='n_string') {
 			$file->write('<c r="'.$cell_name.'" s="'.$cell_style_idx.'" t="inlineStr"><is><t>'.self::xmlspecialchars($value).'</t></is></c>');
-		} elseif ($num_format_type=='n_auto') {
+		} elseif ($num_format_type=='n_auto' || 1) { //auto-detect unknown column types
 			if (!is_string($value) || $value=='0' || ($value[0]!='0' && ctype_digit($value)) || preg_match("/^\-?[1-9][0-9]*(\.[0-9]+)?$/", $value)){
 				$file->write('<c r="'.$cell_name.'" s="'.$cell_style_idx.'" t="n"><v>'.self::xmlspecialchars($value).'</v></c>');//int,float,currency
 			} else { //implied: ($cell_format=='string')
 				$file->write('<c r="'.$cell_name.'" s="'.$cell_style_idx.'" t="inlineStr"><is><t>'.self::xmlspecialchars($value).'</t></is></c>');
 			}
-		} else {
-			$file->write('<c r="'.$cell_name.'" s="'.$cell_style_idx.'"/>');
-			trigger_error("Unknown column type: ".$num_format_type, E_USER_ERROR);
 		}
 	}