diff --git a/mrbgems/mruby-metaprog/test/metaprog.rb b/mrbgems/mruby-metaprog/test/metaprog.rb
index d55c05557..1df239278 100644
--- a/mrbgems/mruby-metaprog/test/metaprog.rb
+++ b/mrbgems/mruby-metaprog/test/metaprog.rb
@@ -193,6 +193,18 @@ assert('Module#class_variable_defined?', '15.2.2.4.16') do
   assert_true Test4ClassVariableDefined.class_variable_defined?(:@@cv)
   assert_false Test4ClassVariableDefined.class_variable_defined?(:@@noexisting)
   assert_raise(NameError) { Test4ClassVariableDefined.class_variable_defined?("@@2") }
+
+  # shared empty iv_tbl (include)
+  m = Module.new
+  c = Class.new{include m}
+  m.class_variable_set(:@@cv2, 2)
+  assert_true c.class_variable_defined?(:@@cv2)
+
+  # shared empty iv_tbl (prepend)
+  m = Module.new
+  c = Class.new{prepend m}
+  m.class_variable_set(:@@cv2, 2)
+  assert_true c.class_variable_defined?(:@@cv2)
 end
 
 assert('Module#class_variable_get', '15.2.2.4.17') do
@@ -205,6 +217,26 @@ assert('Module#class_variable_get', '15.2.2.4.17') do
   %w[@@a? @@! @a a].each do |n|
     assert_raise(NameError) { Test4ClassVariableGet.class_variable_get(n) }
   end
+
+  # shared empty iv_tbl (include)
+  m = Module.new
+  class Test4ClassVariableGet end
+  Test4ClassVariableGet.include m
+  m.class_variable_set(:@@cv2, 2)
+  assert_equal 2, Test4ClassVariableGet.class_variable_get(:@@cv2)
+  class Test4ClassVariableGet
+    assert_equal 2, @@cv2
+  end
+
+  # shared empty iv_tbl (prepend)
+  m = Module.new
+  class Test4ClassVariableGet end
+  Test4ClassVariableGet.prepend m
+  m.class_variable_set(:@@cv2, 2)
+  assert_equal 2, Test4ClassVariableGet.class_variable_get(:@@cv2)
+  class Test4ClassVariableGet
+    assert_equal 2, @@cv2
+  end
 end
 
 assert('Module#class_variable_set', '15.2.2.4.18') do
@@ -241,6 +273,18 @@ assert('Module#class_variables', '15.2.2.4.19') do
 
   assert_equal [:@@var1], Test4ClassVariables1.class_variables
   assert_equal [:@@var2, :@@var1], Test4ClassVariables2.class_variables
+
+  # shared empty iv_tbl (include)
+  m = Module.new
+  c = Class.new{include m}
+  m.class_variable_set(:@@var3, 3)
+  assert_equal [:@@var3], c.class_variables
+
+  # shared empty iv_tbl (prepend)
+  m = Module.new
+  c = Class.new{prepend m}
+  m.class_variable_set(:@@var3, 3)
+  assert_equal [:@@var3], c.class_variables
 end
 
 assert('Module#constants', '15.2.2.4.24') do
@@ -256,6 +300,18 @@ assert('Module#constants', '15.2.2.4.24') do
 
   assert_equal [ :C ], TestA.constants
   assert_equal [ :C, :C2 ], $n
+
+  # shared empty iv_tbl (include)
+  m = Module.new
+  TestC = Class.new{include m}
+  m::C3 = 1
+  assert_equal [ :C3 ], TestC.constants
+
+  # shared empty iv_tbl (prepend)
+  m = Module.new
+  TestC = Class.new{prepend m}
+  m::C3 = 1
+  assert_equal [ :C3 ], TestC.constants
 end
 
 assert('Module#included_modules', '15.2.2.4.30') do
diff --git a/src/class.c b/src/class.c
index cca5f768c..dd614ff56 100644
--- a/src/class.c
+++ b/src/class.c
@@ -1401,7 +1401,6 @@ include_class_new(mrb_state *mrb, struct RClass *m, struct RClass *super)
     m = m->c;
   }
   MRB_CLASS_ORIGIN(m);
-  ic->iv = m->iv;
   ic->mt = m->mt;
   ic->super = super;
   if (m->tt == MRB_TT_ICLASS) {
@@ -1526,7 +1525,6 @@ mrb_prepend_module(mrb_state *mrb, struct RClass *c, struct RClass *m)
     c->super = origin;
     origin->mt = c->mt;
     c->mt = NULL;
-    origin->iv = c->iv;
     mrb_field_write_barrier(mrb, (struct RBasic*)c, (struct RBasic*)origin);
     c->flags |= MRB_FL_CLASS_IS_PREPENDED;
   }
diff --git a/src/variable.c b/src/variable.c
index 3bae38c18..2afbfd93e 100644
--- a/src/variable.c
+++ b/src/variable.c
@@ -296,6 +296,12 @@ obj_iv_p(mrb_value obj)
   }
 }
 
+static iv_tbl*
+class_iv_ptr(struct RClass *c)
+{
+  return c->tt == MRB_TT_ICLASS ? c->c->iv : c->iv;
+}
+
 MRB_API mrb_value
 mrb_obj_iv_get(mrb_state *mrb, struct RObject *obj, mrb_sym sym)
 {
@@ -593,7 +599,7 @@ mrb_mod_class_variables(mrb_state *mrb, mrb_value mod)
   ary = mrb_ary_new(mrb);
   c = mrb_class_ptr(mod);
   while (c) {
-    iv_foreach(mrb, c->iv, cv_i, &ary);
+    iv_foreach(mrb, class_iv_ptr(c), cv_i, &ary);
     if (!inherit) break;
     c = c->super;
   }
@@ -608,7 +614,7 @@ mrb_mod_cv_get(mrb_state *mrb, struct RClass *c, mrb_sym sym)
   int given = FALSE;
 
   while (c) {
-    if (c->iv && iv_get(mrb, c->iv, sym, &v)) {
+    if (iv_get(mrb, class_iv_ptr(c), sym, &v)) {
       given = TRUE;
     }
     c = c->super;
@@ -622,7 +628,7 @@ mrb_mod_cv_get(mrb_state *mrb, struct RClass *c, mrb_sym sym)
     if (c->tt == MRB_TT_CLASS || c->tt == MRB_TT_MODULE) {
       given = FALSE;
       while (c) {
-        if (c->iv && iv_get(mrb, c->iv, sym, &v)) {
+        if (iv_get(mrb, class_iv_ptr(c), sym, &v)) {
           given = TRUE;
         }
         c = c->super;
@@ -647,7 +653,7 @@ mrb_mod_cv_set(mrb_state *mrb, struct RClass *c, mrb_sym sym, mrb_value v)
   struct RClass * cls = c;
 
   while (c) {
-    iv_tbl *t = c->iv;
+    iv_tbl *t = class_iv_ptr(c);
     int pos = iv_get(mrb, t, sym, NULL);
 
     if (pos) {
@@ -674,7 +680,10 @@ mrb_mod_cv_set(mrb_state *mrb, struct RClass *c, mrb_sym sym, mrb_value v)
       break;
     }
   }
-  else{
+  else if (cls && cls->tt == MRB_TT_ICLASS) {
+    c = cls->c;
+  }
+  else {
     c = cls;
   }
 
@@ -697,7 +706,7 @@ mrb_bool
 mrb_mod_cv_defined(mrb_state *mrb, struct RClass * c, mrb_sym sym)
 {
   while (c) {
-    iv_tbl *t = c->iv;
+    iv_tbl *t = class_iv_ptr(c);
     if (iv_get(mrb, t, sym, NULL)) return TRUE;
     c = c->super;
   }
@@ -765,7 +774,7 @@ const_get(mrb_state *mrb, struct RClass *base, mrb_sym sym, mrb_bool skip)
   if (skip) c = c->super;
 L_RETRY:
   while (c) {
-    if (!MRB_FLAG_TEST(c, MRB_FL_CLASS_IS_PREPENDED) && c->iv && iv_get(mrb, c->iv, sym, &v)) {
+    if (!MRB_FLAG_TEST(c, MRB_FL_CLASS_IS_PREPENDED) && iv_get(mrb, class_iv_ptr(c), sym, &v)) {
       return v;
     }
     c = c->super;
@@ -801,14 +810,14 @@ mrb_vm_const_get(mrb_state *mrb, mrb_sym sym)
 
   c = MRB_PROC_TARGET_CLASS(proc);
   if (!c) c = mrb->object_class;
-  if (iv_get(mrb, c->iv, sym, &v)) {
+  if (iv_get(mrb, class_iv_ptr(c), sym, &v)) {
     return v;
   }
   c2 = c;
   while (c2 && c2->tt == MRB_TT_SCLASS) {
     mrb_value klass;
 
-    if (!iv_get(mrb, c2->iv, MRB_SYM(__attached__), &klass)) {
+    if (!iv_get(mrb, class_iv_ptr(c2), MRB_SYM(__attached__), &klass)) {
       c2 = NULL;
       break;
     }
@@ -819,7 +828,7 @@ mrb_vm_const_get(mrb_state *mrb, mrb_sym sym)
   while (proc) {
     c2 = MRB_PROC_TARGET_CLASS(proc);
     if (!c2) c2 = mrb->object_class;
-    if (c2 && iv_get(mrb, c2->iv, sym, &v)) {
+    if (c2 && iv_get(mrb, class_iv_ptr(c2), sym, &v)) {
       return v;
     }
     proc = proc->upper;
@@ -912,7 +921,7 @@ mrb_mod_constants(mrb_state *mrb, mrb_value mod)
   mrb_get_args(mrb, "|b", &inherit);
   ary = mrb_ary_new(mrb);
   while (c) {
-    iv_foreach(mrb, c->iv, const_i, &ary);
+    iv_foreach(mrb, class_iv_ptr(c), const_i, &ary);
     if (!inherit) break;
     c = c->super;
     if (c == mrb->object_class) break;
@@ -988,7 +997,7 @@ const_defined_0(mrb_state *mrb, mrb_value mod, mrb_sym id, mrb_bool exclude, mrb
   tmp = klass;
 retry:
   while (tmp) {
-    if (iv_get(mrb, tmp->iv, id, NULL)) {
+    if (iv_get(mrb, class_iv_ptr(tmp), id, NULL)) {
       return TRUE;
     }
     if (!recurse && (klass != mrb->object_class)) break;
@@ -1047,7 +1056,7 @@ find_class_sym(mrb_state *mrb, struct RClass *outer, struct RClass *c)
   if (outer == c) return 0;
   arg.c = c;
   arg.sym = 0;
-  iv_foreach(mrb, outer->iv, csym_i, &arg);
+  iv_foreach(mrb, class_iv_ptr(outer), csym_i, &arg);
   return arg.sym;
 }
 
diff --git a/test/t/module.rb b/test/t/module.rb
index c18276a9f..ef25f01e2 100644
--- a/test/t/module.rb
+++ b/test/t/module.rb
@@ -231,6 +231,18 @@ assert('Module#const_defined?', '15.2.2.4.20') do
   assert_true Test4ConstDefined.const_defined?(:Const4Test4ConstDefined)
   assert_false Test4ConstDefined.const_defined?(:NotExisting)
   assert_wrong_const_name{ Test4ConstDefined.const_defined?(:wrong_name) }
+
+  # shared empty iv_tbl (include)
+  m = Module.new
+  c = Class.new{include m}
+  m::CONST = 1
+  assert_true c.const_defined?(:CONST)
+
+  # shared empty iv_tbl (prepend)
+  m = Module.new
+  c = Class.new{prepend m}
+  m::CONST = 1
+  assert_true c.const_defined?(:CONST)
 end
 
 assert('Module#const_get', '15.2.2.4.21') do
@@ -246,6 +258,18 @@ assert('Module#const_get', '15.2.2.4.21') do
   assert_uninitialized_const{ Test4ConstGet.const_get(:I_DO_NOT_EXIST) }
   assert_uninitialized_const{ Test4ConstGet.const_get("I_DO_NOT_EXIST::ME_NEITHER") }
   assert_wrong_const_name{ Test4ConstGet.const_get(:wrong_name) }
+
+  # shared empty iv_tbl (include)
+  m = Module.new
+  c = Class.new{include m}
+  m::CONST = 1
+  assert_equal 1, c.const_get(:CONST)
+
+  # shared empty iv_tbl (prepend)
+  m = Module.new
+  c = Class.new{prepend m}
+  m::CONST = 1
+  assert_equal 1, c.const_get(:CONST)
 end
 
 assert('Module#const_set', '15.2.2.4.23') do
@@ -779,7 +803,7 @@ end
 
 assert('module to return the last value') do
   m = module M; :m end
-  assert_equal(m, :m)
+  assert_equal(:m, m)
 end
 
 assert('module to return nil if body is empty') do
@@ -796,3 +820,25 @@ assert('get constant of parent module in singleton class; issue #3568') do
 
   assert_equal("value", actual)
 end
+
+assert('shared empty iv_tbl (include)') do
+  m1 = Module.new
+  m2 = Module.new{include m1}
+  c = Class.new{include m2}
+  m1::CONST1 = 1
+  assert_equal 1, m2::CONST1
+  assert_equal 1, c::CONST1
+  m2::CONST2 = 2
+  assert_equal 2, c::CONST2
+end
+
+assert('shared empty iv_tbl (prepend)') do
+  m1 = Module.new
+  m2 = Module.new{prepend m1}
+  c = Class.new{include m2}
+  m1::CONST1 = 1
+  assert_equal 1, m2::CONST1
+  assert_equal 1, c::CONST1
+  m2::CONST2 = 2
+  assert_equal 2, c::CONST2
+end