diff --git a/cont.c b/cont.c
index c91cae6..532fc3b 100644
--- a/cont.c
+++ b/cont.c
@@ -116,6 +116,8 @@ static const rb_data_type_t cont_data_type, fiber_data_type;
 static VALUE rb_cContinuation;
 static VALUE rb_cFiber;
 static VALUE rb_eFiberError;
+static ID id_default_vm_stacksize;
+static ID id_vm_stacksize;
 
 #define GetContPtr(obj, ptr)  \
     TypedData_Get_Struct((obj), rb_context_t, &cont_data_type, (ptr))
@@ -1016,7 +1018,7 @@ fiber_t_alloc(VALUE fibval)
 }
 
 static VALUE
-fiber_init(VALUE fibval, VALUE proc)
+fiber_init(VALUE fibval, VALUE proc, VALUE vm_stacksize)
 {
     rb_fiber_t *fib = fiber_t_alloc(fibval);
     rb_context_t *cont = &fib->cont;
@@ -1030,7 +1032,7 @@ fiber_init(VALUE fibval, VALUE proc)
 
     fiber_link_join(fib);
 
-    th->stack_size = FIBER_VM_STACK_SIZE;
+    th->stack_size = NUM2ULONG(vm_stacksize);
     th->stack = ALLOC_N(VALUE, th->stack_size);
 
     th->cfp = (void *)(th->stack + th->stack_size);
@@ -1060,16 +1062,32 @@ fiber_init(VALUE fibval, VALUE proc)
 }
 
 /* :nodoc: */
+static VALUE rb_fiber_s_get_default_vm_stacksize(VALUE);
+
 static VALUE
-rb_fiber_init(VALUE fibval)
+rb_fiber_init(int argc, VALUE *argv, VALUE fibval)
 {
-    return fiber_init(fibval, rb_block_proc());
+    VALUE opt;
+    VALUE stacksize;
+
+    rb_scan_args(argc, argv, "0:", &opt);
+    if (NIL_P(opt) || NIL_P(rb_hash_aref(opt, ID2SYM(id_vm_stacksize))))
+	stacksize = rb_fiber_s_get_default_vm_stacksize(rb_obj_class(fibval));
+    else
+	stacksize = rb_to_int(rb_hash_aref(opt, ID2SYM(id_vm_stacksize)));
+    if (NUM2ULONG(stacksize) < (unsigned long)FIBER_VM_STACK_SIZE)
+	rb_raise(rb_eArgError,
+		 "Fiber vm stacksize must equal or bigger than %d",
+		 FIBER_VM_STACK_SIZE);
+
+    return fiber_init(fibval, rb_block_proc(), stacksize);
 }
 
 VALUE
 rb_fiber_new(VALUE (*func)(ANYARGS), VALUE obj)
 {
-    return fiber_init(fiber_alloc(rb_cFiber), rb_proc_new(func, obj));
+    return fiber_init(fiber_alloc(rb_cFiber), rb_proc_new(func, obj),
+		      rb_fiber_s_get_default_vm_stacksize(rb_cFiber));
 }
 
 static VALUE
@@ -1396,6 +1414,20 @@ rb_fiber_m_transfer(int argc, VALUE *argv, VALUE fib)
 
 /*
  *  call-seq:
+ *    fiber.vm_stacksize() -> integer
+ *
+ *  Returns VM stack size of the fiber.
+ */
+static VALUE
+rb_fiber_vm_stacksize(VALUE fibval)
+{
+    rb_fiber_t *fib;
+    GetFiberPtr(fibval, fib);
+    return ULONG2NUM(fib->cont.saved_thread.stack_size);
+}
+
+/*
+ *  call-seq:
  *     Fiber.yield(args, ...) -> obj
  *
  *  Yields control back to the context that resumed the fiber, passing
@@ -1424,7 +1456,39 @@ rb_fiber_s_current(VALUE klass)
     return rb_fiber_current();
 }
 
+/*
+ *  call-seq:
+ *    Fiber.default_vm_stacksize() -> integer
+ *
+ *  Returns the default VM stack size. Note that this is a maximum number of
+ *  object in VM stack, not a size in byte.
+ */
+static VALUE
+rb_fiber_s_get_default_vm_stacksize(VALUE klass)
+{
+	return rb_ivar_get(klass, id_default_vm_stacksize);
+}
 
+/*
+ *  call-seq:
+ *    Fiber.default_vm_stacksize = num -> integer
+ *
+ *  Sets the default VM stack size.
+ *  Returns +num+.
+ *  Raises TypeError if +num+ is not Numeric and
+ *  raises ArgumentError if num is less than FIBER_VM_STACK_SIZE.
+ */
+static VALUE
+rb_fiber_s_set_default_vm_stacksize(VALUE klass, VALUE num)
+{
+	num = rb_to_int(num);
+	if (NUM2ULONG(num) < (unsigned long)FIBER_VM_STACK_SIZE)
+	    rb_raise(rb_eArgError,
+		     "Fiber default_vm_stacksize must equal or bigger than %d",
+		     FIBER_VM_STACK_SIZE);
+	rb_ivar_set(klass, id_default_vm_stacksize, num);
+	return num;
+}
 
 /*
  *  Document-class: FiberError
@@ -1455,12 +1519,22 @@ Init_Cont(void)
     SET_MACHINE_STACK_END(&th->machine_stack_end);
 #endif
 
+    id_default_vm_stacksize = rb_intern("default_vm_stacksize");
+    id_vm_stacksize = rb_intern("vm_stacksize");
+
     rb_cFiber = rb_define_class("Fiber", rb_cObject);
     rb_define_alloc_func(rb_cFiber, fiber_alloc);
     rb_eFiberError = rb_define_class("FiberError", rb_eStandardError);
+    rb_ivar_set(rb_cFiber, id_default_vm_stacksize,
+		INT2NUM(FIBER_VM_STACK_SIZE));
+    rb_define_singleton_method(rb_cFiber, "default_vm_stacksize",
+			       rb_fiber_s_get_default_vm_stacksize, 0);
+    rb_define_singleton_method(rb_cFiber, "default_vm_stacksize=",
+			       rb_fiber_s_set_default_vm_stacksize, 1);
     rb_define_singleton_method(rb_cFiber, "yield", rb_fiber_s_yield, -1);
-    rb_define_method(rb_cFiber, "initialize", rb_fiber_init, 0);
+    rb_define_method(rb_cFiber, "initialize", rb_fiber_init, -1);
     rb_define_method(rb_cFiber, "resume", rb_fiber_m_resume, -1);
+    rb_define_method(rb_cFiber, "vm_stacksize", rb_fiber_vm_stacksize, 0);
 }
 
 #if defined __GNUC__ && __GNUC__ >= 4
diff --git a/test/ruby/test_fiber.rb b/test/ruby/test_fiber.rb
index ed7ecc7..0248f3c 100644
--- a/test/ruby/test_fiber.rb
+++ b/test/ruby/test_fiber.rb
@@ -220,5 +220,37 @@ class TestFiber < Test::Unit::TestCase
     end
     assert_equal("Can't call on top of Fiber or Thread", error.message, bug5083)
   end
+
+  def test_default_vm_stacksize
+    begin
+      default_vm_stacksize = Fiber.default_vm_stacksize
+      assert_equal(4*1024, default_vm_stacksize)
+      Fiber.default_vm_stacksize = 8 * 1024
+      assert_equal(8*1024, Fiber.default_vm_stacksize)
+      assert_raise(TypeError) do
+        Fiber.default_vm_stacksize = Object.new
+      end
+      assert_raise(ArgumentError) do
+        Fiber.default_vm_stacksize = 0
+      end
+    ensure
+      if default_vm_stacksize
+        Fiber.default_vm_stacksize = default_vm_stacksize
+      end
+    end
+  end
+
+  def test_vm_stacksize
+    fib = Fiber.new { }
+    assert_equal(Fiber.default_vm_stacksize, fib.vm_stacksize)
+    fib = Fiber.new(:vm_stacksize => 8*1024) {}
+    assert_equal(8*1024, fib.vm_stacksize)
+    assert_raise(TypeError) do
+      Fiber.new(:vm_stacksize => Object.new) {}
+    end
+    assert_raise(ArgumentError) do
+      Fiber.new(:vm_stacksize => 2 * 1024) {}
+    end
+  end
 end