Enforce unsafe surrounding block on safe-to-call functions
diff --git a/demo/src/main.rs b/demo/src/main.rs
index 10f57e5..dca596a 100644
--- a/demo/src/main.rs
+++ b/demo/src/main.rs
@@ -14,7 +14,7 @@
     }
 
     // C++ types and signatures exposed to Rust.
-    extern "C++" {
+    unsafe extern "C++" {
         include!("demo/include/blobstore.h");
 
         type BlobstoreClient;