diff --git a/hash.c b/hash.c
index f951d59e96..132af403a7 100644
--- a/hash.c
+++ b/hash.c
@@ -6251,19 +6251,6 @@ env_key(VALUE dmy, VALUE value)
     return Qnil;
 }
 
-/*
- * call-seq:
- *   ENV.index(value) -> name
- *
- * Deprecated method that is equivalent to ENV.key.
- */
-static VALUE
-env_index(VALUE dmy, VALUE value)
-{
-    rb_warn_deprecated("ENV.index", "ENV.key");
-    return env_key(dmy, value);
-}
-
 static VALUE
 env_to_hash(void)
 {
@@ -7137,7 +7124,6 @@ Init_Hash(void)
     rb_define_singleton_method(envtbl, "to_a", env_to_a, 0);
     rb_define_singleton_method(envtbl, "to_s", env_to_s, 0);
     rb_define_singleton_method(envtbl, "key", env_key, 1);
-    rb_define_singleton_method(envtbl, "index", env_index, 1);
     rb_define_singleton_method(envtbl, "size", env_size, 0);
     rb_define_singleton_method(envtbl, "length", env_size, 0);
     rb_define_singleton_method(envtbl, "empty?", env_empty_p, 0);
diff --git a/spec/ruby/core/env/index_spec.rb b/spec/ruby/core/env/index_spec.rb
index 43875f5a50..dfa40b6139 100644
--- a/spec/ruby/core/env/index_spec.rb
+++ b/spec/ruby/core/env/index_spec.rb
@@ -1,12 +1,14 @@
 require_relative '../../spec_helper'
 require_relative 'shared/key'
 
-describe "ENV.index" do
-  it_behaves_like :env_key, :index
+ruby_version_is ''...'2.8' do
+  describe "ENV.index" do
+    it_behaves_like :env_key, :index
 
-  it "warns about deprecation" do
-    -> do
-      ENV.index("foo")
-    end.should complain(/warning: ENV.index is deprecated; use ENV.key/)
+    it "warns about deprecation" do
+      -> do
+        ENV.index("foo")
+      end.should complain(/warning: ENV.index is deprecated; use ENV.key/)
+    end
   end
 end
diff --git a/test/ruby/test_env.rb b/test/ruby/test_env.rb
index c1109cb2ef..7735b53045 100644
--- a/test/ruby/test_env.rb
+++ b/test/ruby/test_env.rb
@@ -84,7 +84,6 @@ class TestEnv < Test::Unit::TestCase
     ENV['test'] = val[0...-1]
 
     assert_nil(ENV.key(val))
-    assert_nil(ENV.index(val))
     assert_nil(ENV.key(val.upcase))
     ENV['test'] = val
     if IGNORE_CASE