diff --git a/compiler/cpp/src/main.h b/compiler/cpp/src/main.h
index 8751dd5..98ca754 100644
--- a/compiler/cpp/src/main.h
+++ b/compiler/cpp/src/main.h
@@ -102,6 +102,13 @@
 void emit_byte_type_warning();
 
 /**
+ * Prints deprecation notice for old NS declarations that are no longer supported
+ * 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 = NULL);
+
+/**
  * Flex utilities
  */