diff --git a/gcc/diagnostic.h b/gcc/diagnostic.h
index edd221f1a8ce..423e07230a65 100644
--- a/gcc/diagnostic.h
+++ b/gcc/diagnostic.h
@@ -220,7 +220,6 @@ public:
 };
 
 class edit_context;
-namespace json { class value; }
 class diagnostic_client_data_hooks;
 class logical_location;
 class diagnostic_diagram;