diff --git a/.cargo/config b/.cargo/config
index 7f9d89b452..584d158f1c 100644
--- a/.cargo/config
+++ b/.cargo/config
@@ -2,3 +2,9 @@
 test-gen-llvm = "test -p test_gen"
 test-gen-dev = "test -p roc_gen_dev -p test_gen --no-default-features --features gen-dev"
 test-gen-wasm = "test -p roc_gen_wasm -p test_gen --no-default-features --features gen-wasm"
+
+[target.wasm32-unknown-unknown]
+# Rust compiler flags for minimum-sized .wasm binary in the web REPL
+# opt-level=s   Optimizations should focus more on size than speed
+# lto=fat       Spend extra effort on link-time optimization across crates
+rustflags = ["-Copt-level=s", "-Clto=fat"]
diff --git a/repl_wasm/Cargo.toml b/repl_wasm/Cargo.toml
index 944d550955..61dad966be 100644
--- a/repl_wasm/Cargo.toml
+++ b/repl_wasm/Cargo.toml
@@ -26,7 +26,6 @@ roc_target = {path = "../compiler/roc_target"}
 roc_types = {path = "../compiler/types"}
 
 [features]
-default = ["console_error_panic_hook"]
 wasmer = ["futures"]
 
 [package.metadata.wasm-pack.profile.profiling]
diff --git a/repl_wasm/src/lib.rs b/repl_wasm/src/lib.rs
index 0d1c6d9461..a1d66e6f8d 100644
--- a/repl_wasm/src/lib.rs
+++ b/repl_wasm/src/lib.rs
@@ -3,7 +3,7 @@ mod repl;
 //
 // Interface with external JS in the browser
 //
-#[cfg(not(feature = "wasmer"))]
+#[cfg(feature = "console_error_panic_hook")]
 extern crate console_error_panic_hook;
 #[cfg(not(feature = "wasmer"))]
 mod externs_js;
diff --git a/repl_wasm/src/repl.rs b/repl_wasm/src/repl.rs
index 9bbd2891af..95cb77be11 100644
--- a/repl_wasm/src/repl.rs
+++ b/repl_wasm/src/repl.rs
@@ -155,7 +155,7 @@ impl<'a> ReplApp<'a> for WasmReplApp<'a> {
 }
 
 pub async fn entrypoint_from_js(src: String) -> Result<String, String> {
-    #[cfg(not(feature = "wasmer"))]
+    #[cfg(feature = "console_error_panic_hook")]
     console_error_panic_hook::set_once();
 
     let arena = &Bump::new();
diff --git a/repl_www/build.sh b/repl_www/build.sh
index 52a2121631..d9e157271c 100755
--- a/repl_www/build.sh
+++ b/repl_www/build.sh
@@ -26,11 +26,11 @@ cp -r repl_www/public/* $WWW_ROOT
 if [ -n "${REPL_DEBUG:-}" ]
 then
     # Leave out wasm-opt since it takes too long when debugging, and provide some debug options
-    cargo build --target wasm32-unknown-unknown -p roc_repl_wasm --release
+    cargo build --target wasm32-unknown-unknown -p roc_repl_wasm --release --features console_error_panic_hook
     wasm-bindgen --target web --keep-debug target/wasm32-unknown-unknown/release/roc_repl_wasm.wasm --out-dir repl_wasm/pkg/
 else
     # A `--profiling` build is optimized and has debug info, so we get stack traces for compiler `todo!()`
-    wasm-pack build --profiling --target web repl_wasm
+    wasm-pack build --profiling --target web repl_wasm -- --features console_error_panic_hook
 fi
 
 cp repl_wasm/pkg/*.wasm $WWW_ROOT