diff --git a/tool/src/cpp/ty.rs b/tool/src/cpp/ty.rs
index 2918af88f..92e774e6e 100644
--- a/tool/src/cpp/ty.rs
+++ b/tool/src/cpp/ty.rs
@@ -61,7 +61,7 @@ pub(super) struct TyGenContext<'ccx, 'tcx, 'header> {
     pub generating_struct_fields: bool,
 }
 
-impl<'ccx, 'tcx> TyGenContext<'ccx, 'tcx, '_> {
+impl<'ccx, 'tcx: 'ccx> TyGenContext<'ccx, 'tcx, '_> {
     /// Adds an enum definition to the current decl and impl headers.
     ///
     /// The enum is defined in C++ using a `class` with a single private field that is the