diff --git a/poincare/include/poincare/expression.h b/poincare/include/poincare/expression.h
index e77947f57..e98c0e1c8 100644
--- a/poincare/include/poincare/expression.h
+++ b/poincare/include/poincare/expression.h
@@ -18,7 +18,7 @@ class Expression {
       Subtraction,
       Symbol
     };
-    static Expression * parse(char * string);
+    static Expression * parse(char const * string);
     virtual ~Expression();
 
     //virtual Expression ** children() = 0; // NULL-terminated
diff --git a/poincare/src/expression.cpp b/poincare/src/expression.cpp
index 05a25d311..10b9e5e0a 100644
--- a/poincare/src/expression.cpp
+++ b/poincare/src/expression.cpp
@@ -14,7 +14,7 @@ int poincare_expression_yyparse(yyscan_t scanner, Expression ** expressionOutput
 Expression::~Expression() {
 }
 
-Expression * Expression::parse(char * string) {
+Expression * Expression::parse(char const * string) {
   void * scanner;
   poincare_expression_yylex_init(&scanner);
   YY_BUFFER_STATE buf = poincare_expression_yy_scan_string(string, scanner);