Include BaseTsd.h to get SSIZE_T
diff --git a/gen/write.rs b/gen/write.rs
index 9d6ef6e..d80e957 100644
--- a/gen/write.rs
+++ b/gen/write.rs
@@ -126,6 +126,7 @@
                 needs_rust_fn = true;
             }
             ty if ty == Isize => {
+                out.include.base_tsd = true;
                 needs_rust_isize = true;
             }
             ty if ty == RustString => {