diff --git a/Dockerfile b/Dockerfile
index 313ccdf3..49788e0d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -9,8 +9,9 @@ RUN cargo install --locked wasm-bindgen-cli
 # will cause Docker to re-run `cargo build` even when the source hasn't changed.
 COPY src/ ./src
 COPY Cargo.toml ./Cargo.toml
+COPY Cargo.lock
 
-RUN cargo build --target wasm32-unknown-unknown --profile=wasm-release
+RUN cargo build --locked --target wasm32-unknown-unknown --profile=wasm-release
 RUN wasm-bindgen --no-typescript --target web --out-dir ./out/ --out-name "boids" target/wasm32-unknown-unknown/wasm-release/another-boids-in-rust.wasm
 COPY www/index.html out/index.html