4 files changed, 15 insertions, 6 deletions
diff --git a/ops/fast_call.rs b/ops/fast_call.rs
index a7ca51d4f..12ff9e446 100644
--- a/ops/fast_call.rs
+++ b/ops/fast_call.rs
@@ -250,13 +250,14 @@ pub(crate) fn generate(
       //
       // V8 calls the slow path so we can take the slot
       // value and throw.
-      let result_wrap = q!(Vars { op_state }, {
+      let default = optimizer.fast_result.as_ref().unwrap().default_value();
+      let result_wrap = q!(Vars { op_state, default }, {
         match result {
           Ok(result) => result,
           Err(err) => {
             op_state.last_fast_op_error.replace(err);
             __opts.fallback = true;
-            Default::default()
+            default
           }
         }
       });
diff --git a/ops/optimizer.rs b/ops/optimizer.rs
index a3ccd51b3..115011008 100644
--- a/ops/optimizer.rs
+++ b/ops/optimizer.rs
@@ -217,8 +217,8 @@ fn get_fast_scalar(s: &str) -> Option<FastValue> {
     "bool" => Some(FastValue::Bool),
     "u32" => Some(FastValue::U32),
     "i32" => Some(FastValue::I32),
-    "u64" => Some(FastValue::U64),
-    "i64" => Some(FastValue::I64),
+    "u64" | "usize" => Some(FastValue::U64),
+    "i64" | "isize" => Some(FastValue::I64),
     "f32" => Some(FastValue::F32),
     "f64" => Some(FastValue::F64),
     "* const c_void" | "* mut c_void" => Some(FastValue::Pointer),
@@ -254,6 +254,16 @@ pub(crate) enum FastValue {
   Float64Array,
 }
 
+impl FastValue {
+  pub fn default_value(&self) -> Quote {
+    match self {
+      FastValue::Pointer => q!({ ::std::ptr::null_mut() }),
+      FastValue::Void => q!({}),
+      _ => q!({ Default::default() }),
+    }
+  }
+}
+
 impl Default for FastValue {
   fn default() -> Self {
     Self::Void
diff --git a/ops/optimizer_tests/unit_result.out b/ops/optimizer_tests/unit_result.out
index f9d1e0c34..f4e87ffa3 100644
--- a/ops/optimizer_tests/unit_result.out
+++ b/ops/optimizer_tests/unit_result.out
@@ -107,7 +107,6 @@ fn op_unit_result_fast_fn<'scope>(
         Err(err) => {
             op_state.last_fast_op_error.replace(err);
             __opts.fallback = true;
-            Default::default()
         }
     }
 }
diff --git a/ops/optimizer_tests/unit_result2.out b/ops/optimizer_tests/unit_result2.out
index e297befcb..d1df0e041 100644
--- a/ops/optimizer_tests/unit_result2.out
+++ b/ops/optimizer_tests/unit_result2.out
@@ -142,7 +142,6 @@ fn op_set_nodelay_fast_fn<'scope>(
         Err(err) => {
             state.last_fast_op_error.replace(err);
             __opts.fallback = true;
-            Default::default()
         }
     }
 }