diff --git a/build/src/main.rs b/build/src/main.rs
index eaa54bc..083266f 100644
--- a/build/src/main.rs
+++ b/build/src/main.rs
@@ -78,7 +78,11 @@ fn main() {
 	process_output(target_dir, wasm_binary).expect("Failed to process cargo target directory");
 
 	let path = wasm_path(target_dir, wasm_binary);
-	let mut module =  parity_wasm::deserialize_file(&path).unwrap();
+
+	let mut module = wasm_utils::externalize(
+		parity_wasm::deserialize_file(&path).unwrap(),
+		vec!["_free", "_malloc"],
+	);
 
 	wasm_utils::optimize(&mut module, vec!["_call"]).expect("Optimizer to finish without errors");