diff --git a/Writer/Parser.php b/Writer/Parser.php
index e16acf7..ad2ad66 100644
--- a/Writer/Parser.php
+++ b/Writer/Parser.php
@@ -552,12 +552,12 @@ class Spreadsheet_Excel_Writer_Parser extends PEAR
             return $this->_convertRef2d($token);
         }
         // match external references like Sheet1!A1 or Sheet1:Sheet2!A1
-        elseif (preg_match("/^\w+(\:\w+)?\![A-Ia-i]?[A-Za-z](\d+)$/",$token))
+        elseif (preg_match("/^\w+(\:\w+)?\![A-Ia-i]?[A-Za-z](\d+)$/u",$token))
         {
             return $this->_convertRef3d($token);
         }
         // match external references like 'Sheet1'!A1 or 'Sheet1:Sheet2'!A1
-        elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\![A-Ia-i]?[A-Za-z](\d+)$/",$token))
+        elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\![A-Ia-i]?[A-Za-z](\d+)$/u",$token))
         {
             return $this->_convertRef3d($token);
         }
@@ -572,12 +572,12 @@ class Spreadsheet_Excel_Writer_Parser extends PEAR
             return $this->_convertRange2d($token);
         }
         // match external ranges like Sheet1!A1 or Sheet1:Sheet2!A1:B2
-        elseif (preg_match("/^\w+(\:\w+)?\!([A-Ia-i]?[A-Za-z])?(\d+)\:([A-Ia-i]?[A-Za-z])?(\d+)$/",$token))
+        elseif (preg_match("/^\w+(\:\w+)?\!([A-Ia-i]?[A-Za-z])?(\d+)\:([A-Ia-i]?[A-Za-z])?(\d+)$/u",$token))
         {
             return $this->_convertRange3d($token);
         }
         // match external ranges like 'Sheet1'!A1 or 'Sheet1:Sheet2'!A1:B2
-        elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\!([A-Ia-i]?[A-Za-z])?(\d+)\:([A-Ia-i]?[A-Za-z])?(\d+)$/",$token))
+        elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\!([A-Ia-i]?[A-Za-z])?(\d+)\:([A-Ia-i]?[A-Za-z])?(\d+)$/u",$token))
         {
             return $this->_convertRange3d($token);
         }
@@ -1222,14 +1222,14 @@ class Spreadsheet_Excel_Writer_Parser extends PEAR
                     return $token;
                 }
                 // If it's an external reference (Sheet1!A1 or Sheet1:Sheet2!A1)
-                elseif (preg_match("/^\w+(\:\w+)?\![A-Ia-i]?[A-Za-z][0-9]+$/",$token) and
+                elseif (preg_match("/^\w+(\:\w+)?\![A-Ia-i]?[A-Za-z][0-9]+$/u",$token) and
                        !ereg("[0-9]",$this->_lookahead) and
                        ($this->_lookahead != ':') and ($this->_lookahead != '.'))
                 {
                     return $token;
                 }
                 // If it's an external reference ('Sheet1'!A1 or 'Sheet1:Sheet2'!A1)
-                elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\![A-Ia-i]?[A-Za-z][0-9]+$/",$token) and
+                elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\![A-Ia-i]?[A-Za-z][0-9]+$/u",$token) and
                        !ereg("[0-9]",$this->_lookahead) and
                        ($this->_lookahead != ':') and ($this->_lookahead != '.'))
                 {
@@ -1248,13 +1248,13 @@ class Spreadsheet_Excel_Writer_Parser extends PEAR
                     return $token;
                 }
                 // If it's an external range like Sheet1!A1 or Sheet1:Sheet2!A1:B2
-                elseif (preg_match("/^\w+(\:\w+)?\!([A-Ia-i]?[A-Za-z])?[0-9]+:([A-Ia-i]?[A-Za-z])?[0-9]+$/",$token) and
+                elseif (preg_match("/^\w+(\:\w+)?\!([A-Ia-i]?[A-Za-z])?[0-9]+:([A-Ia-i]?[A-Za-z])?[0-9]+$/u",$token) and
                        !ereg("[0-9]",$this->_lookahead))
                 {
                     return $token;
                 }
                 // If it's an external range like 'Sheet1'!A1 or 'Sheet1:Sheet2'!A1:B2
-                elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\!([A-Ia-i]?[A-Za-z])?[0-9]+:([A-Ia-i]?[A-Za-z])?[0-9]+$/",$token) and
+                elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\!([A-Ia-i]?[A-Za-z])?[0-9]+:([A-Ia-i]?[A-Za-z])?[0-9]+$/u",$token) and
                        !ereg("[0-9]",$this->_lookahead))
                 {
                     return $token;
@@ -1489,14 +1489,14 @@ class Spreadsheet_Excel_Writer_Parser extends PEAR
             return $result;
         }
         // If it's an external reference (Sheet1!A1 or Sheet1:Sheet2!A1)
-        elseif (preg_match("/^\w+(\:\w+)?\![A-Ia-i]?[A-Za-z][0-9]+$/",$this->_current_token))
+        elseif (preg_match("/^\w+(\:\w+)?\![A-Ia-i]?[A-Za-z][0-9]+$/u",$this->_current_token))
         {
             $result = $this->_createTree($this->_current_token, '', '');
             $this->_advance();
             return $result;
         }
         // If it's an external reference ('Sheet1'!A1 or 'Sheet1:Sheet2'!A1)
-        elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\![A-Ia-i]?[A-Za-z][0-9]+$/",$this->_current_token))
+        elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\![A-Ia-i]?[A-Za-z][0-9]+$/u",$this->_current_token))
         {
             $result = $this->_createTree($this->_current_token, '', '');
             $this->_advance();
@@ -1511,14 +1511,14 @@ class Spreadsheet_Excel_Writer_Parser extends PEAR
             return $result;
         }
         // If it's an external range (Sheet1!A1 or Sheet1!A1:B2)
-        elseif (preg_match("/^\w+(\:\w+)?\!([A-Ia-i]?[A-Za-z])?[0-9]+:([A-Ia-i]?[A-Za-z])?[0-9]+$/",$this->_current_token))
+        elseif (preg_match("/^\w+(\:\w+)?\!([A-Ia-i]?[A-Za-z])?[0-9]+:([A-Ia-i]?[A-Za-z])?[0-9]+$/u",$this->_current_token))
         {
             $result = $this->_current_token;
             $this->_advance();
             return $result;
         }
         // If it's an external range ('Sheet1'!A1 or 'Sheet1'!A1:B2)
-        elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\!([A-Ia-i]?[A-Za-z])?[0-9]+:([A-Ia-i]?[A-Za-z])?[0-9]+$/",$this->_current_token))
+        elseif (preg_match("/^'[\w -]+(\:[\w -]+)?'\!([A-Ia-i]?[A-Za-z])?[0-9]+:([A-Ia-i]?[A-Za-z])?[0-9]+$/u",$this->_current_token))
         {
             $result = $this->_current_token;
             $this->_advance();