diff --git a/Cargo.toml b/Cargo.toml
index d6c2eff2..1ff7b9ae 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,8 +14,8 @@ base64-simd  = "0.8"
 cssparser    = "0.29"
 infer        = "0.16"
 libavif      = { version = "0.14", default-features = false, features = ["codec-aom"] }
-napi         = { version = "3.0.0-alpha.19", default-features = false, features = ["napi3", "serde-json"] }
-napi-derive  = { version = "3.0.0-alpha.17", default-features = false }
+napi         = { version = "3.0.0-alpha.20", default-features = false, features = ["napi3", "serde-json"] }
+napi-derive  = { version = "3.0.0-alpha.18", default-features = false }
 nom          = "7"
 num_cpus     = "1"
 regex        = "1"
diff --git a/build.rs b/build.rs
index 60fed6f8..be98ef63 100644
--- a/build.rs
+++ b/build.rs
@@ -22,8 +22,12 @@ fn main() {
       env::set_var("CXX", "clang-cl");
     }
     _ => {
-      env::set_var("CC", "clang");
-      env::set_var("CXX", "clang++");
+      if env::var("CC").is_err() {
+        env::set_var("CC", "clang");
+      }
+      if env::var("CXX").is_err() {
+        env::set_var("CXX", "clang++");
+      }
     }
   }
 
diff --git a/src/image.rs b/src/image.rs
index b7a487e7..56a3c33e 100644
--- a/src/image.rs
+++ b/src/image.rs
@@ -114,7 +114,7 @@ impl ImageData {
   }
 }
 
-#[napi]
+#[napi(custom_finalize)]
 pub struct Image {
   pub(crate) bitmap: Option<Bitmap>,
   pub(crate) complete: bool,
@@ -127,6 +127,15 @@ pub struct Image {
   pub(crate) src: Option<Uint8Array>,
 }
 
+impl ObjectFinalize for Image {
+  fn finalize(self, env: Env) -> Result<()> {
+    if let Some(bitmap) = self.bitmap {
+      env.adjust_external_memory(-(bitmap.0.width as i64) * (bitmap.0.height as i64) * 4)?;
+    }
+    Ok(())
+  }
+}
+
 #[napi]
 impl Image {
   #[napi(constructor)]
@@ -239,7 +248,7 @@ impl Image {
       height: self.height,
       color_space: self.color_space,
       data: Some(data),
-      this_ref: env.create_reference(&*this)?,
+      this_ref: Ref::new(&env, &*this)?,
     };
     let task_output = env.spawn(decoder)?;
 
@@ -442,6 +451,7 @@ impl Task for BitmapDecoder {
         self_mut.src = self.data.take();
         self_mut.is_svg = bitmap.is_svg;
         self_mut.bitmap = Some(bitmap.data);
+        env.adjust_external_memory((output.width as i64) * (output.height as i64) * 4)?;
       }
       DecodeStatus::Empty => {}
       DecodeStatus::InvalidSvg => {