diff --git a/poincare/src/expression_lexer.l b/poincare/src/expression_lexer.l
index 62e80b7d9..be1537876 100644
--- a/poincare/src/expression_lexer.l
+++ b/poincare/src/expression_lexer.l
@@ -83,7 +83,7 @@ using namespace Poincare;
    * starting with \x. */
 
 [0-9]+ { poincare_expression_yylval.string.address = yytext; poincare_expression_yylval.string.length = yyleng; return DIGITS; }
-[A-Zxyztn] { poincare_expression_yylval.character = yytext[0]; return SYMBOL; }
+[A-Za-z] { poincare_expression_yylval.character = yytext[0]; return SYMBOL; }
 M[0-9] { poincare_expression_yylval.character = Symbol::matrixSymbol(yytext[1]); return SYMBOL; }
 u\(n\) { poincare_expression_yylval.character = Symbol::SpecialSymbols::un; return SYMBOL; }
 u\(n\+1\) { poincare_expression_yylval.character = Symbol::SpecialSymbols::un1; return SYMBOL; }