diff --git a/gc/mmtk/mmtk.c b/gc/mmtk/mmtk.c
index dbb3545..60bbbfc 100644
--- a/gc/mmtk/mmtk.c
+++ b/gc/mmtk/mmtk.c
@@ -57,6 +57,7 @@ struct objspace {
 
     uintptr_t vo_bit_log_region_size;
     uintptr_t vo_bit_base_addr;
+    size_t max_non_los_default_alloc_bytes;
 };
 
 #define OBJ_FREE_BUF_CAPACITY 128
@@ -110,6 +111,7 @@ RB_THREAD_LOCAL_SPECIFIER VALUE marking_parent_object;
 #include <pthread.h>
 
 #define MMTK_ALLOCATION_SEMANTICS_DEFAULT 0
+#define MMTK_ALLOCATION_SEMANTICS_LOS 2
 
 static inline VALUE rb_mmtk_call_object_closure(VALUE obj, bool pin);
 
@@ -604,6 +606,7 @@ rb_gc_impl_objspace_init(void *objspace_ptr)
 
     objspace->vo_bit_log_region_size = mmtk_get_vo_bit_log_region_size();
     objspace->vo_bit_base_addr = mmtk_get_vo_bit_base_addr();
+    objspace->max_non_los_default_alloc_bytes = mmtk_max_non_los_default_alloc_bytes();
 }
 
 void
@@ -670,8 +673,6 @@ void rb_gc_impl_set_params(void *objspace_ptr) { }
 
 static VALUE gc_verify_internal_consistency(VALUE self) { return Qnil; }
 
-#define MMTK_MAX_OBJ_SIZE 1024
-
 static inline size_t
 rb_mmtk_align_obj_size(size_t object_size)
 {
@@ -685,12 +686,12 @@ rb_gc_impl_zjit_new_obj_fastpath(void *objspace_ptr, size_t alloc_size, VALUE fl
 #if USE_ZJIT && RB_GC_OBJ_SUFFIX_SIZE == 0
     struct objspace *objspace = objspace_ptr;
 
-    if (alloc_size > MMTK_MAX_OBJ_SIZE) return false;
-
     size_t total_size = rb_mmtk_align_obj_size(alloc_size + sizeof(VALUE) + RB_GC_OBJ_SUFFIX_SIZE);
     size_t object_size = total_size - sizeof(VALUE) - RB_GC_OBJ_SUFFIX_SIZE;
     size_t value_size_shift = sizeof(VALUE) == 8 ? 3 : 2;
 
+    if (total_size > objspace->max_non_los_default_alloc_bytes) return false;
+
     struct rb_gc_zjit_mmtk_new_obj_fastpath mmtk_fastpath = {
         objspace,
         offsetof(struct objspace, total_allocated_objects),
@@ -730,7 +731,6 @@ rb_gc_impl_init(void)
     rb_hash_aset(gc_constants, ID2SYM(rb_intern("RVALUE_SIZE")), SIZET2NUM(sizeof(struct RBasic) + sizeof(VALUE[RBIMPL_RVALUE_EMBED_LEN_MAX])));
     rb_hash_aset(gc_constants, ID2SYM(rb_intern("RBASIC_SIZE")), SIZET2NUM(sizeof(struct RBasic)));
     rb_hash_aset(gc_constants, ID2SYM(rb_intern("RVALUE_OVERHEAD")), INT2NUM(0));
-    rb_hash_aset(gc_constants, ID2SYM(rb_intern("RVARGC_MAX_ALLOCATE_SIZE")), LONG2FIX(MMTK_MAX_OBJ_SIZE));
     // TODO: correctly set RVALUE_OLD_AGE when we have generational GC support
     rb_hash_aset(gc_constants, ID2SYM(rb_intern("RVALUE_OLD_AGE")), INT2FIX(0));
     OBJ_FREEZE(gc_constants);
@@ -960,22 +960,27 @@ rb_gc_impl_new_obj(void *objspace_ptr, void *cache_ptr, VALUE klass, VALUE flags
     struct objspace *objspace = objspace_ptr;
     struct MMTk_ractor_cache *ractor_cache = cache_ptr;
 
-    if (alloc_size == 0 || alloc_size > MMTK_MAX_OBJ_SIZE) {
-        rb_bug("rb_gc_impl_new_obj: allocation size too large (size=%"PRIuSIZE")", alloc_size);
+    if (alloc_size == 0) {
+        rb_bug("rb_gc_impl_new_obj: allocation size out of range (size=%"PRIuSIZE")", alloc_size);
     }
 
     // Layout: [hidden size header (sizeof(VALUE))][payload (alloc_size)][suffix (RB_GC_OBJ_SUFFIX_SIZE)]
     size_t total_size = rb_mmtk_align_obj_size(alloc_size + sizeof(VALUE) + RB_GC_OBJ_SUFFIX_SIZE);
     size_t object_size = total_size - sizeof(VALUE) - RB_GC_OBJ_SUFFIX_SIZE;
+    MMTk_AllocationSemantics semantics = total_size > objspace->max_non_los_default_alloc_bytes
+        ? MMTK_ALLOCATION_SEMANTICS_LOS
+        : MMTK_ALLOCATION_SEMANTICS_DEFAULT;
     *actual_alloc_size = object_size;
 
     if (objspace->gc_stress) {
         mmtk_handle_user_collection_request(ractor_cache, false, false);
     }
 
-    VALUE *alloc_obj = (VALUE *)rb_mmtk_alloc_fast_path(objspace, ractor_cache, total_size, MMTk_MIN_OBJ_ALIGN);
+    VALUE *alloc_obj = semantics == MMTK_ALLOCATION_SEMANTICS_DEFAULT
+        ? (VALUE *)rb_mmtk_alloc_fast_path(objspace, ractor_cache, total_size, MMTk_MIN_OBJ_ALIGN)
+        : NULL;
     if (!alloc_obj) {
-        alloc_obj = mmtk_alloc(ractor_cache->mutator, total_size, MMTk_MIN_OBJ_ALIGN, 0, MMTK_ALLOCATION_SEMANTICS_DEFAULT);
+        alloc_obj = mmtk_alloc(ractor_cache->mutator, total_size, MMTk_MIN_OBJ_ALIGN, 0, semantics);
 
         // On heap exhaustion raise NoMemoryError.
         if (RB_UNLIKELY(alloc_obj == NULL)) {
@@ -988,8 +993,8 @@ rb_gc_impl_new_obj(void *objspace_ptr, void *cache_ptr, VALUE klass, VALUE flags
     alloc_obj[0] = flags;
     alloc_obj[1] = klass;
 
-    if (ractor_cache->bump_pointer == NULL) {
-        mmtk_post_alloc(ractor_cache->mutator, (void*)alloc_obj, object_size, MMTK_ALLOCATION_SEMANTICS_DEFAULT);
+    if (semantics == MMTK_ALLOCATION_SEMANTICS_LOS || ractor_cache->bump_pointer == NULL) {
+        mmtk_post_alloc(ractor_cache->mutator, (void*)alloc_obj, total_size, semantics);
     }
     else {
         // We can use the post alloc fast path if we're using Immix bump pointer allocator
@@ -1013,7 +1018,7 @@ rb_gc_impl_obj_slot_size(VALUE obj)
 size_t
 rb_gc_impl_size_slot_size(void *objspace_ptr, size_t size)
 {
-    if (size == 0 || size > MMTK_MAX_OBJ_SIZE) {
+    if (size == 0) {
         rb_bug("rb_gc_impl_size_slot_size: size too large (size=%"PRIuSIZE")", size);
     }
 
@@ -1023,13 +1028,13 @@ rb_gc_impl_size_slot_size(void *objspace_ptr, size_t size)
 bool
 rb_gc_impl_size_allocatable_p(size_t size)
 {
-    return size <= MMTK_MAX_OBJ_SIZE;
+    return true;
 }
 
 size_t
 rb_gc_impl_max_allocation_size(void)
 {
-    return MMTK_MAX_OBJ_SIZE;
+    return SIZE_MAX;
 }
 
 // Malloc
diff --git a/gc/mmtk/mmtk.h b/gc/mmtk/mmtk.h
index 42edeb1..7f330b8 100644
--- a/gc/mmtk/mmtk.h
+++ b/gc/mmtk/mmtk.h
@@ -115,6 +115,8 @@ void mmtk_set_gc_enabled(bool enable);
 
 bool mmtk_gc_enabled_p(void);
 
+size_t mmtk_max_non_los_default_alloc_bytes(void);
+
 MMTk_Address mmtk_alloc(MMTk_Mutator *mutator,
                         size_t size,
                         size_t align,
diff --git a/gc/mmtk/src/api.rs b/gc/mmtk/src/api.rs
index 936baf7..e8770d4 100644
--- a/gc/mmtk/src/api.rs
+++ b/gc/mmtk/src/api.rs
@@ -314,6 +314,14 @@ pub extern "C" fn mmtk_gc_enabled_p() -> bool {
 
 // =============== Object allocation ===============
 
+#[no_mangle]
+pub extern "C" fn mmtk_max_non_los_default_alloc_bytes() -> usize {
+    mmtk()
+        .get_plan()
+        .constraints()
+        .max_non_los_default_alloc_bytes
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn mmtk_alloc(
     mutator: *mut RubyMutator,
diff --git a/test/.excludes-mmtk/TestStruct/SubStruct.rb b/test/.excludes-mmtk/TestStruct/SubStruct.rb
new file mode 100644
index 0000000..709cd0f
--- /dev/null
+++ b/test/.excludes-mmtk/TestStruct/SubStruct.rb
@@ -0,0 +1 @@
+exclude(:test_larger_than_largest_pool, "depends on max slot size")
diff --git a/test/.excludes-mmtk/TestStruct/TopStruct.rb b/test/.excludes-mmtk/TestStruct/TopStruct.rb
new file mode 100644
index 0000000..709cd0f
--- /dev/null
+++ b/test/.excludes-mmtk/TestStruct/TopStruct.rb
@@ -0,0 +1 @@
+exclude(:test_larger_than_largest_pool, "depends on max slot size")
diff --git a/test/.excludes-mmtk/Test_StringCapacity.rb b/test/.excludes-mmtk/Test_StringCapacity.rb
new file mode 100644
index 0000000..59b47a5
--- /dev/null
+++ b/test/.excludes-mmtk/Test_StringCapacity.rb
@@ -0,0 +1,7 @@
+exclude(:test_capacity_embedded, "depends on max slot size")
+exclude(:test_capacity_frozen, "depends on max slot size")
+exclude(:test_capacity_fstring, "depends on max slot size")
+exclude(:test_capacity_normal, "depends on max slot size")
+exclude(:test_io_read, "depends on max slot size")
+exclude(:test_literal_capacity, "depends on max slot size")
+exclude(:test_s_new_capacity, "depends on max slot size")