diff --git a/compiler/cpp/src/main.cc b/compiler/cpp/src/main.cc
index 5e218b4..1b3b633 100644
--- a/compiler/cpp/src/main.cc
+++ b/compiler/cpp/src/main.cc
@@ -661,8 +661,8 @@
  * If new_form is NULL, old_form is assumed to be a language identifier, such as "cpp"
  * If new_form is not NULL, both arguments are used exactly as given
  */
-void error_unsupported_namespace_decl(char* old_form, char* new_form) {
-  char* remainder = "";
+void error_unsupported_namespace_decl(const char* old_form, const char* new_form) {
+  const char* remainder = "";
   if( new_form == NULL) {
     new_form = old_form;
     remainder = "_namespace";