diff --git a/Cargo.lock b/Cargo.lock
index 4f2510b..353ed10 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -35,7 +35,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "basic-lang"
-version = "0.3.0"
+version = "0.4.0"
 dependencies = [
  "ansi_term 0.12.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "ctrlc 3.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/Cargo.toml b/Cargo.toml
index 3c790ca..983433b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "basic-lang"
-version = "0.3.0"
+version = "0.4.0"
 authors = ["David Turnbull"]
 license = "Apache-2.0 OR MIT"
 readme = "README.md"
@@ -12,6 +12,9 @@ edition = "2018"
 
 [profile.release]
 panic = "abort"
+opt-level = 'z'
+lto = true
+codegen-units = 1
 
 [dependencies]
 ansi_term = "0.12"