diff --git a/test/ruby/test_refinement.rb b/test/ruby/test_refinement.rb
index c0754d8cf0..56f33ae00a 100644
--- a/test/ruby/test_refinement.rb
+++ b/test/ruby/test_refinement.rb
@@ -1206,6 +1206,41 @@ class TestRefinement < Test::Unit::TestCase
     INPUT
   end
 
+  def test_refined_protected_methods
+    assert_separately([], <<-"end;")
+    bug18806 = '[ruby-core:108705] [Bug #18806]'
+    class C; end
+
+    module R
+      refine C do
+        def refined_call_foo = foo
+        def refined_call_foo_on(other) = other.foo
+
+        protected
+
+        def foo = :foo
+      end
+    end
+
+    class C
+      using R
+
+      def call_foo = foo
+      def call_foo_on(other) = other.foo
+    end
+
+    c = C.new
+    assert_equal :foo, c.call_foo, bug18806
+    assert_equal :foo, c.call_foo_on(c), bug18806
+    assert_equal :foo, c.call_foo_on(C.new), bug18806
+
+    using R
+    assert_equal :foo, c.refined_call_foo, bug18806
+    assert_equal :foo, c.refined_call_foo_on(c), bug18806
+    assert_equal :foo, c.refined_call_foo_on(C.new), bug18806
+    end;
+  end
+
   def test_refine_basic_object
     assert_separately([], <<-"end;")
     bug10106 = '[ruby-core:64166] [Bug #10106]'
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 09fcd2f729..d2f3fc62bd 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -3711,6 +3711,19 @@ vm_call_method_nome(rb_execution_context_t *ec, rb_control_frame_t *cfp, struct
     }
 }
 
+/* Protected method calls and super invocations need to check that the receiver
+ * (self for super) inherits the module on which the method is defined.
+ * In the case of refinements, it should consider the original class not the
+ * refinement.
+ */
+static VALUE
+vm_defined_class_for_protected_call(const rb_callable_method_entry_t *me)
+{
+    VALUE defined_class = me->defined_class;
+    VALUE refined_class = RCLASS_REFINED_CLASS(defined_class);
+    return NIL_P(refined_class) ? defined_class : refined_class;
+}
+
 static inline VALUE
 vm_call_method(rb_execution_context_t *ec, rb_control_frame_t *cfp, struct rb_calling_info *calling)
 {
@@ -3737,7 +3750,8 @@ vm_call_method(rb_execution_context_t *ec, rb_control_frame_t *cfp, struct rb_ca
 
 	  case METHOD_VISI_PROTECTED:
 	    if (!(vm_ci_flag(ci) & VM_CALL_OPT_SEND)) {
-		if (!rb_obj_is_kind_of(cfp->self, vm_cc_cme(cc)->defined_class)) {
+                VALUE defined_class = vm_defined_class_for_protected_call(vm_cc_cme(cc));
+                if (!rb_obj_is_kind_of(cfp->self, defined_class)) {
                     vm_cc_method_missing_reason_set(cc, MISSING_PROTECTED);
                     return vm_call_method_missing(ec, cfp, calling);
 		}
@@ -3834,11 +3848,7 @@ vm_search_super_method(const rb_control_frame_t *reg_cfp, struct rb_call_data *c
 	vm_super_outside();
     }
 
-    current_defined_class = me->defined_class;
-
-    if (!NIL_P(RCLASS_REFINED_CLASS(current_defined_class))) {
-	current_defined_class = RCLASS_REFINED_CLASS(current_defined_class);
-    }
+    current_defined_class = vm_defined_class_for_protected_call(me);
 
     if (BUILTIN_TYPE(current_defined_class) != T_MODULE &&
         reg_cfp->iseq != method_entry_iseqptr(me) &&