diff --git a/Cargo.toml b/Cargo.toml
index f9455aed3..9c6e6e9d4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -45,6 +45,9 @@ wasm-opt = ['-Oz', '-g']
 # Tell cargo to run `rustc` with `-C debuginfo=2` - ie, to include debug symbols.
 # https://doc.rust-lang.org/cargo/reference/profiles.html#debug
 debug = true
+# Tell cargo to run `rustc` with `-Oz` - ie, to optimize for size.
+# https://doc.rust-lang.org/cargo/reference/profiles.html#opt-level
+opt-level = 'z'
 
 [lib]
 crate-type = ["cdylib"]
diff --git a/scripts/build.sh b/scripts/build.sh
index 72b92b7e7..d0036524c 100755
--- a/scripts/build.sh
+++ b/scripts/build.sh
@@ -16,7 +16,7 @@ set -e
 
 cd $(dirname "$0")/..
 
-RUSTFLAGS='-C opt-level=z' WASM_BINDGEN_WEAKREF=1 wasm-pack build --target nodejs --scope matrix-org --out-dir pkg "${WASM_PACK_ARGS[@]}"
+wasm-pack build --target nodejs --scope matrix-org --out-dir pkg --weak-refs "${WASM_PACK_ARGS[@]}"
 
 # Convert the Wasm into a JS file that exports the base64'ed Wasm.
 {