diff --git a/lib/rbs/collection/config/lockfile_generator.rb b/lib/rbs/collection/config/lockfile_generator.rb
index c742f963a..f85d1980f 100644
--- a/lib/rbs/collection/config/lockfile_generator.rb
+++ b/lib/rbs/collection/config/lockfile_generator.rb
@@ -10,6 +10,7 @@ class LockfileGenerator
           "base64" => nil,
           "bigdecimal" => nil,
           "csv" => nil,
+          "kconv" => nil,
           "minitest" => nil,
           "net-smtp" => nil,
           "nkf" => nil,
@@ -172,8 +173,8 @@ def generate
           return if lockfile.gems.key?(name)
 
           case name
-          when 'bigdecimal-math'
-            # The `bigdecimal-math` is never released as a gem.
+          when 'bigdecimal-math', 'kconv'
+            # These gems are never released as a gem.
             # Therefore, `assign_gem` should not be called.
             RBS.logger.info {
               from = from_gem || "rbs_collection.yaml"
diff --git a/test/stdlib/Kconv_test.rb b/test/stdlib/Kconv_test.rb
deleted file mode 100644
index 4cac08c3e..000000000
--- a/test/stdlib/Kconv_test.rb
+++ /dev/null
@@ -1,118 +0,0 @@
-require_relative "test_helper"
-require "kconv"
-
-class KconvSingletonTest < Test::Unit::TestCase
-  include TestHelper
-
-  library "kconv"
-  testing "singleton(::Kconv)"
-
-  def test_ASCII
-    assert_const_type "::Encoding", "Kconv::ASCII"
-  end
-
-  def test_AUTO
-    assert_const_type "nil", "Kconv::AUTO"
-  end
-
-  def test_BINARY
-    assert_const_type "::Encoding", "Kconv::BINARY"
-  end
-
-  def test_EUC
-    assert_const_type "::Encoding", "Kconv::EUC"
-  end
-
-  def test_JIS
-    assert_const_type "::Encoding", "Kconv::JIS"
-  end
-
-  def test_NOCONV
-    assert_const_type "nil", "Kconv::NOCONV"
-  end
-
-  def test_SJIS
-    assert_const_type "::Encoding", "Kconv::SJIS"
-  end
-
-  def test_UNKNOWN
-    assert_const_type "nil", "Kconv::UNKNOWN"
-  end
-
-  def test_UTF16
-    assert_const_type "::Encoding", "Kconv::UTF16"
-  end
-
-  def test_UTF32
-    assert_const_type "::Encoding", "Kconv::UTF32"
-  end
-
-  def test_UTF8
-    assert_const_type "::Encoding", "Kconv::UTF8"
-  end
-
-  def test_guess
-    assert_send_type "(::String str) -> ::Encoding?",
-                     Kconv, :guess, ""
-  end
-
-  def test_iseuc
-    assert_send_type "(::String str) -> bool",
-                     Kconv, :iseuc, ""
-  end
-
-  def test_isjis
-    assert_send_type "(::String str) -> bool",
-                     Kconv, :isjis, ""
-  end
-
-  def test_issjis
-    assert_send_type "(::String str) -> bool",
-                     Kconv, :issjis, ""
-  end
-
-  def test_isutf8
-    assert_send_type "(::String str) -> bool",
-                     Kconv, :isutf8, ""
-  end
-
-  def test_kconv
-    assert_send_type "(::String str, ::Encoding? out_code, ?::Encoding? in_code) -> ::String",
-                     Kconv, :kconv, "", Kconv::UTF8
-  end
-
-  def test_toeuc
-    assert_send_type "(::String str) -> ::String",
-                     Kconv, :toeuc, ""
-  end
-
-  def test_tojis
-    assert_send_type "(::String str) -> ::String",
-                     Kconv, :tojis, ""
-  end
-
-  def test_tolocale
-    assert_send_type "(::String str) -> ::String",
-                     Kconv, :tolocale, ""
-  end
-
-  def test_tosjis
-    assert_send_type "(::String str) -> ::String",
-                     Kconv, :tosjis, ""
-  end
-
-  def test_toutf16
-    assert_send_type "(::String str) -> ::String",
-                     Kconv, :toutf16, ""
-  end
-
-  def test_toutf32
-    assert_send_type "(::String str) -> ::String",
-                     Kconv, :toutf32, ""
-  end
-
-  def test_toutf8
-    assert_send_type "(::String str) -> ::String",
-                     Kconv, :toutf8, ""
-  end
-end