diff --git a/winch/filetests/build.rs b/winch/filetests/build.rs
new file mode 100644
index 0000000000..bd0f62b29d
--- /dev/null
+++ b/winch/filetests/build.rs
@@ -0,0 +1,4 @@
+fn main() {
+    // Ensure that new files in the filetests directory cause a rebuild.
+    println!("cargo:rerun-if-changed=filetests");
+}