diff --git a/src/SimpleXLSXGen.php b/src/SimpleXLSXGen.php
index 0d0b346..1ebe59c 100644
--- a/src/SimpleXLSXGen.php
+++ b/src/SimpleXLSXGen.php
@@ -214,7 +214,7 @@ class SimpleXLSXGen {
 							$ct = 's'; // shared string
 							$v = str_replace(['&','<','>'],['&amp;','&lt;','&gt;'], $v);
 							$cv = false;
-							if ( isset($SI_KEYS[$v]) ) {
+							if ( isset($SI_KEYS[$v]) && $SI_KEYS[$v] === $v ) {
 								$cv = $SI_KEYS[$v];
 							}