diff --git a/bindgen/src/bindings/cpp/templates/scaffolding.hpp b/bindgen/src/bindings/cpp/templates/scaffolding.hpp
index c6b4175..97c1fba 100644
--- a/bindgen/src/bindings/cpp/templates/scaffolding.hpp
+++ b/bindgen/src/bindings/cpp/templates/scaffolding.hpp
@@ -6,6 +6,8 @@
 extern "C" {
 #endif
 
+#ifndef UNIFFI_CPP_INTERNALSTRUCTS
+#define UNIFFI_CPP_INTERNALSTRUCTS
 struct ForeignBytes {
     int32_t len;
     uint8_t *data;
@@ -22,6 +24,8 @@ struct RustCallStatus {
     RustBuffer error_buf;
 };
 
+#endif
+
 typedef int ForeignCallback(uint64_t handle, uint32_t method, uint8_t *args_data, int32_t args_len, RustBuffer *buf_ptr);
 
 {% for func in ci.iter_ffi_function_definitions() %}