diff --git a/Gemfile b/Gemfile
index f4a8b0da7..1dc3e88ab 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,7 +1,8 @@
 source "https://rubygems.org"
 
-group :development do
-  gem "rake"
-  gem "rake-compiler"
-  gem "test-unit", "~> 3.0", ">= 3.4.6"
-end
+gem "rake"
+gem "rake-compiler"
+gem "test-unit", "~> 3.0", ">= 3.4.6"
+gem "test-unit-ruby-core"
+gem "prime"
+gem "rdoc"
diff --git a/test/openssl/test_ossl.rb b/test/openssl/test_ossl.rb
index e1d86bd40..95634ce0a 100644
--- a/test/openssl/test_ossl.rb
+++ b/test/openssl/test_ossl.rb
@@ -1,8 +1,6 @@
 # frozen_string_literal: true
 require_relative "utils"
 
-require 'benchmark'
-
 if defined?(OpenSSL)
 
 class OpenSSL::OSSL < OpenSSL::SSLTestCase
@@ -54,8 +52,14 @@ def test_memcmp_timing
 
     a_b_time = a_c_time = 0
     100.times do
-      a_b_time += Benchmark.measure { 100.times { OpenSSL.fixed_length_secure_compare(a, b) } }.real
-      a_c_time += Benchmark.measure { 100.times { OpenSSL.fixed_length_secure_compare(a, c) } }.real
+      t1 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+      100.times { OpenSSL.fixed_length_secure_compare(a, b) }
+      t2 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+      100.times { OpenSSL.fixed_length_secure_compare(a, c) }
+      t3 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+
+      a_b_time += t2 - t1
+      a_c_time += t3 - t2
     end
     assert_operator(a_b_time, :<, a_c_time * 10, "fixed_length_secure_compare timing test failed")
     assert_operator(a_c_time, :<, a_b_time * 10, "fixed_length_secure_compare timing test failed")