rust::Vec has a bitcopy constructor too
diff --git a/gen/src/write.rs b/gen/src/write.rs
index d5eae90..12f2839 100644
--- a/gen/src/write.rs
+++ b/gen/src/write.rs
@@ -244,7 +244,7 @@
         writeln!(out, "// #include \"rust/cxx.h\"");
     }
 
-    if needs_rust_string {
+    if needs_rust_string || needs_rust_vec {
         out.next_section();
         writeln!(out, "struct unsafe_bitcopy_t;");
     }