diff --git a/gc/mmtk/mmtk.c b/gc/mmtk/mmtk.c
index 6547a6c..b28cb28 100644
--- a/gc/mmtk/mmtk.c
+++ b/gc/mmtk/mmtk.c
@@ -576,7 +576,6 @@ rb_gc_impl_objspace_alloc(void)
 {
     MMTk_Builder *builder = rb_mmtk_builder_init();
     MMTk_RubyBindingOptions binding_options = {
-        .ractor_check_mode = RACTOR_CHECK_MODE != 0,
         .suffix_size = RVALUE_SUFFIX_SIZE,
     };
     mmtk_init_binding(builder, &binding_options, &ruby_upcalls);
diff --git a/gc/mmtk/mmtk.h b/gc/mmtk/mmtk.h
index e8f9592..b11e287 100644
--- a/gc/mmtk/mmtk.h
+++ b/gc/mmtk/mmtk.h
@@ -33,7 +33,6 @@ typedef struct MMTk_BumpPointer {
 #define MMTk_GC_THREAD_KIND_WORKER 1
 
 typedef struct MMTk_RubyBindingOptions {
-    bool ractor_check_mode;
     size_t suffix_size;
 } MMTk_RubyBindingOptions;
 
diff --git a/gc/mmtk/src/abi.rs b/gc/mmtk/src/abi.rs
index c880302..30890e0 100644
--- a/gc/mmtk/src/abi.rs
+++ b/gc/mmtk/src/abi.rs
@@ -291,7 +291,6 @@ impl From<Vec<ObjectReference>> for RawVecOfObjRef {
 #[repr(C)]
 #[derive(Clone)]
 pub struct RubyBindingOptions {
-    pub ractor_check_mode: bool,
     pub suffix_size: usize,
 }