diff --git a/src/fast_api.rs b/src/fast_api.rs
index 3ca7bbaf..d4db8b87 100644
--- a/src/fast_api.rs
+++ b/src/fast_api.rs
@@ -91,6 +91,7 @@ pub enum CType {
   Float32,
   Float64,
   V8Value,
+  SeqOneByteString,
   // https://github.com/v8/v8/blob/492a32943bc34a527f42df2ae15a77154b16cc84/include/v8-fast-api-calls.h#L264-L267
   // kCallbackOptionsType is not part of the Type enum
   // because it is only used internally. Use value 255 that is larger
@@ -110,6 +111,7 @@ pub enum Type {
   Float32,
   Float64,
   V8Value,
+  SeqOneByteString,
   CallbackOptions,
   Sequence(CType),
   TypedArray(CType),
@@ -128,6 +130,7 @@ impl From<&Type> for CType {
       Type::Float32 => CType::Float32,
       Type::Float64 => CType::Float64,
       Type::V8Value => CType::V8Value,
+      Type::SeqOneByteString => CType::SeqOneByteString,
       Type::CallbackOptions => CType::CallbackOptions,
       Type::Sequence(ty) => *ty,
       Type::TypedArray(ty) => *ty,
@@ -204,6 +207,25 @@ pub struct FastApiTypedArray<T: Default> {
   data: *mut T,
 }
 
+#[repr(C)]
+pub struct FastApiOneByteString {
+  data: *const u8,
+  pub length: usize,
+}
+
+impl FastApiOneByteString {
+  #[inline(always)]
+  pub fn as_str(&self) -> &str {
+    // SAFETY: The string is guaranteed to be valid UTF-8.
+    unsafe {
+      std::str::from_utf8_unchecked(std::slice::from_raw_parts(
+        self.data,
+        self.length,
+      ))
+    }
+  }
+}
+
 impl<T: Default> FastApiTypedArray<T> {
   #[inline(always)]
   pub fn get(&self, index: usize) -> T {
diff --git a/tests/test_api.rs b/tests/test_api.rs
index 8f1530f2..1b281e26 100644
--- a/tests/test_api.rs
+++ b/tests/test_api.rs
@@ -8603,3 +8603,73 @@ fn test_detach_key() {
     assert!(buffer.was_detached());
   }
 }
+
+#[test]
+fn test_fast_calls_onebytestring() {
+  static mut WHO: &str = "none";
+  fn fast_fn(
+    _recv: v8::Local<v8::Object>,
+    data: *const fast_api::FastApiOneByteString,
+  ) -> u32 {
+    unsafe { WHO = "fast" };
+    let data = unsafe { &*data }.as_str();
+    assert_eq!("hello", data);
+    data.len() as u32
+  }
+
+  pub struct FastTest;
+  impl fast_api::FastFunction for FastTest {
+    fn args(&self) -> &'static [fast_api::Type] {
+      &[fast_api::Type::V8Value, fast_api::Type::SeqOneByteString]
+    }
+
+    fn return_type(&self) -> fast_api::CType {
+      fast_api::CType::Uint32
+    }
+
+    fn function(&self) -> *const c_void {
+      fast_fn as _
+    }
+  }
+
+  fn slow_fn(
+    _: &mut v8::HandleScope,
+    _: v8::FunctionCallbackArguments,
+    _: v8::ReturnValue,
+  ) {
+    unsafe { WHO = "slow" };
+  }
+
+  let _setup_guard = setup();
+  let isolate = &mut v8::Isolate::new(Default::default());
+  let scope = &mut v8::HandleScope::new(isolate);
+  let context = v8::Context::new(scope);
+  let scope = &mut v8::ContextScope::new(scope, context);
+
+  let global = context.global(scope);
+
+  let template =
+    v8::FunctionTemplate::builder(slow_fn).build_fast(scope, &FastTest, None);
+
+  let name = v8::String::new(scope, "func").unwrap();
+  let value = template.get_function(scope).unwrap();
+  global.set(scope, name.into(), value.into()).unwrap();
+  let source = r#"
+  function f(data) { return func(data); }
+  %PrepareFunctionForOptimization(f);
+  const str = "hello";
+  f(str);
+"#;
+  eval(scope, source).unwrap();
+  assert_eq!("slow", unsafe { WHO });
+
+  let source = r#"
+    %OptimizeFunctionOnNextCall(f);
+    const result = f(str);
+    if (result != 5) {
+      throw new Error("wrong result");
+    }
+  "#;
+  eval(scope, source).unwrap();
+  assert_eq!("fast", unsafe { WHO });
+}