diff --git a/load.c b/load.c
index b85a247c18..1c1fe1afa1 100644
--- a/load.c
+++ b/load.c
@@ -447,6 +447,11 @@ get_loaded_features_index(vm_ns_t *vm_ns)
         VALUE previous_realpath_map = rb_hash_dup(realpath_map);
         rb_hash_clear(realpaths);
         rb_hash_clear(realpath_map);
+
+        /* We have to make a copy of features here because the StringValue call
+         * below could call a Ruby method, which could modify $LOADED_FEATURES
+         * and cause it to be corrupt. */
+        features = rb_ary_resurrect(features);
         for (i = 0; i < RARRAY_LEN(features); i++) {
             VALUE entry, as_str;
             as_str = entry = rb_ary_entry(features, i);
@@ -456,6 +461,10 @@ get_loaded_features_index(vm_ns_t *vm_ns)
                 rb_ary_store(features, i, as_str);
             features_index_add(vm_ns, as_str, INT2FIX(i));
         }
+        /* The user modified $LOADED_FEATURES, so we should restore the changes. */
+        if (!rb_ary_shared_with_p(features, CURRENT_NS_LOADED_FEATURES(vm_ns))) {
+            rb_ary_replace(CURRENT_NS_LOADED_FEATURES(vm_ns), features);
+        }
         reset_loaded_features_snapshot(vm_ns);
 
         features = CURRENT_NS_LOADED_FEATURES_SNAPSHOT(vm_ns);
diff --git a/test/ruby/test_require.rb b/test/ruby/test_require.rb
index 13e7076391..3b6cc1178d 100644
--- a/test/ruby/test_require.rb
+++ b/test/ruby/test_require.rb
@@ -840,6 +840,30 @@ class TestRequire < Test::Unit::TestCase
         p :ok
       end;
     }
+
+    # [Bug #21567]
+    assert_separately(%w[-rtempfile], "#{<<~"begin;"}\n#{<<~"end;"}")
+    begin;
+      class MyString
+        def initialize(path)
+          @path = path
+        end
+
+        def to_str
+          $LOADED_FEATURES.clear
+          @path
+        end
+
+        def to_path = @path
+      end
+
+      def create_ruby_file = Tempfile.create(["test", ".rb"]).path
+
+      require MyString.new(create_ruby_file)
+      $LOADED_FEATURES.unshift(create_ruby_file)
+      $LOADED_FEATURES << MyString.new(create_ruby_file)
+      require create_ruby_file
+    end;
   end
 
   def test_loading_fifo_threading_raise