diff --git a/README.md b/README.md
index d00dacb..326f961 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# SimpleXLSXGen class 0.9.17 (Official)
+# SimpleXLSXGen class 0.9.18 (Official)
 [<img src="https://img.shields.io/endpoint.svg?url=https%3A%2F%2Fshieldsio-patreon.herokuapp.com%2Fshuchkin" />](https://www.patreon.com/shuchkin) [<img src="https://img.shields.io/github/license/shuchkin/simplexlsxgen" />](https://github.com/shuchkin/simplexlsxgen/blob/master/license.md) [<img src="https://img.shields.io/github/stars/shuchkin/simplexlsxgen" />](https://github.com/shuchkin/simplexlsxgen/stargazers) [<img src="https://img.shields.io/github/forks/shuchkin/simplexlsxgen" />](https://github.com/shuchkin/simplexlsxgen/network) [<img src="https://img.shields.io/github/issues/shuchkin/simplexlsxgen" />](https://github.com/shuchkin/simplexlsxgen/issues)
 
 Export data to Excel XLSX file. PHP XLSX generator. No external tools and libraries.<br/>
@@ -62,6 +62,7 @@ SimpleXLSXGen::fromArray( $data )->saveAs('debug.xlsx');
 
 
 ## History
+v0.9.18 (2020-08-22) fixed fast shared strings index<br/> 
 v0.9.17 (2020-08-21) Fixed real numbers in 123.45 format detection, fast shared strings index (thx fredriksundin)<br/> 
 v0.9.16 (2020-07-29) Fixed time detection in HH:MM:SS format<br/>
 v0.9.15 (2020-07-14) escape of shared strings for special chars in cells [#1](https://github.com/shuchkin/simplexlsxgen/issues/1) <br/>
diff --git a/src/SimpleXLSXGen.php b/src/SimpleXLSXGen.php
index 337511b..d06b2cf 100644
--- a/src/SimpleXLSXGen.php
+++ b/src/SimpleXLSXGen.php
@@ -188,9 +188,9 @@ class SimpleXLSXGen {
 
 					if ( is_string($v) ) {
 
-						if ( preg_match( '/^[-+]?\d{1,18}$/', $v ) ) {
+						if ( preg_match( '/^[-+]?[1-9]\d{0,17}$/', $v ) ) {
 							$cv = ltrim($v,'+');
-						} elseif ( preg_match('/^[-+]?\d+\.\d+$/', $v ) ) {
+						} elseif ( preg_match('/^[-+]?(0|[1-9]\d*)\.\d+$/', $v ) ) {
 							$cv = ltrim($v,'+');
 						} elseif ( preg_match('/^([-+]?\d+)%$/', $v, $m) ) {
 							$cv = round( $m[1] / 100, 2);
@@ -214,14 +214,15 @@ class SimpleXLSXGen {
 							$ct = 's'; // shared string
 							$v = str_replace(['&','<','>'],['&amp;','&lt;','&gt;'], $v);
 							$cv = false;
-							if ( isset($SI_KEYS[$v]) ) {
-								$cv = $SI_KEYS[$v];
+							$skey = '~'.$v;
+							if ( isset($SI_KEYS[ $skey ]) ) {
+								$cv = $SI_KEYS[ $skey ];
 							}
 
 							if ( $cv === false ) {
 								$SI[] = $v;
 								$cv  = count( $SI ) - 1;
-								$SI_KEYS[$v] = $cv;
+								$SI_KEYS[$skey] = $cv;
 							}
 						}
 					} elseif ( is_int( $v ) || is_float( $v ) ) {