diff --git a/lib/rb/lib/thrift.rb b/lib/rb/lib/thrift.rb
index 0f58122..5d83695 100644
--- a/lib/rb/lib/thrift.rb
+++ b/lib/rb/lib/thrift.rb
@@ -23,7 +23,6 @@
 $:.unshift File.dirname(__FILE__)
 
 require 'thrift/bytes'
-require 'thrift/core_ext'
 require 'thrift/exceptions'
 require 'thrift/types'
 require 'thrift/processor'
diff --git a/lib/rb/lib/thrift/core_ext.rb b/lib/rb/lib/thrift/core_ext.rb
deleted file mode 100644
index f763cd5..0000000
--- a/lib/rb/lib/thrift/core_ext.rb
+++ /dev/null
@@ -1,23 +0,0 @@
-#
-# Licensed to the Apache Software Foundation (ASF) under one
-# or more contributor license agreements. See the NOTICE file
-# distributed with this work for additional information
-# regarding copyright ownership. The ASF licenses this file
-# to you under the Apache License, Version 2.0 (the
-# "License"); you may not use this file except in compliance
-# with the License. You may obtain a copy of the License at
-#
-#   http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing,
-# software distributed under the License is distributed on an
-# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
-# KIND, either express or implied. See the License for the
-# specific language governing permissions and limitations
-# under the License.
-#
-
-Dir[File.dirname(__FILE__) + "/core_ext/*.rb"].each do |file|
-  name = File.basename(file, '.rb')
-  require "thrift/core_ext/#{name}"
-end
diff --git a/lib/rb/lib/thrift/core_ext/fixnum.rb b/lib/rb/lib/thrift/core_ext/fixnum.rb
deleted file mode 100644
index b4fc90d..0000000
--- a/lib/rb/lib/thrift/core_ext/fixnum.rb
+++ /dev/null
@@ -1,29 +0,0 @@
-# 
-# Licensed to the Apache Software Foundation (ASF) under one
-# or more contributor license agreements. See the NOTICE file
-# distributed with this work for additional information
-# regarding copyright ownership. The ASF licenses this file
-# to you under the Apache License, Version 2.0 (the
-# "License"); you may not use this file except in compliance
-# with the License. You may obtain a copy of the License at
-# 
-#   http://www.apache.org/licenses/LICENSE-2.0
-# 
-# Unless required by applicable law or agreed to in writing,
-# software distributed under the License is distributed on an
-# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
-# KIND, either express or implied. See the License for the
-# specific language governing permissions and limitations
-# under the License.
-#
-
-# Versions of ruby pre 1.8.7 do not have an .ord method available in the Fixnum
-# class.
-#
-if RUBY_VERSION < "1.8.7"
-  class Fixnum
-    def ord
-      self
-    end
-  end
-end
\ No newline at end of file
diff --git a/lib/rb/lib/thrift/protocol/base_protocol.rb b/lib/rb/lib/thrift/protocol/base_protocol.rb
index 4d83a21..e9ea7c2 100644
--- a/lib/rb/lib/thrift/protocol/base_protocol.rb
+++ b/lib/rb/lib/thrift/protocol/base_protocol.rb
@@ -251,9 +251,9 @@
     #
     # Returns nothing.
     def write_type(field_info, value)
-      # if field_info is a Fixnum, assume it is a Thrift::Types constant
+      # if field_info is a Integer, assume it is a Thrift::Types constant
       # convert it into a field_info Hash for backwards compatibility
-      if field_info.is_a? Fixnum
+      if field_info.is_a? Integer
         field_info = {:type => field_info}
       end
 
@@ -291,9 +291,9 @@
     #
     # Returns the value read; object type varies based on field_info[:type].
     def read_type(field_info)
-      # if field_info is a Fixnum, assume it is a Thrift::Types constant
+      # if field_info is a Integer, assume it is a Thrift::Types constant
       # convert it into a field_info Hash for backwards compatibility
-      if field_info.is_a? Fixnum
+      if field_info.is_a? Integer
         field_info = {:type => field_info}
       end
 
diff --git a/lib/rb/lib/thrift/transport/base_transport.rb b/lib/rb/lib/thrift/transport/base_transport.rb
index 97e5935..12dd673 100644
--- a/lib/rb/lib/thrift/transport/base_transport.rb
+++ b/lib/rb/lib/thrift/transport/base_transport.rb
@@ -62,7 +62,7 @@
       raise NotImplementedError
     end
 
-    # Returns an unsigned byte as a Fixnum in the range (0..255).
+    # Returns an unsigned byte as a Integer in the range (0..255).
     def read_byte
       buf = read_all(1)
       return Bytes.get_string_byte(buf, 0)
diff --git a/lib/rb/spec/struct_spec.rb b/lib/rb/spec/struct_spec.rb
index bbd502b..9a4baa8 100644
--- a/lib/rb/spec/struct_spec.rb
+++ b/lib/rb/spec/struct_spec.rb
@@ -227,7 +227,7 @@
     it "should support optional type-checking in Thrift::Struct.new" do
       Thrift.type_checking = true
       begin
-        expect { SpecNamespace::Hello.new(:greeting => 3) }.to raise_error(Thrift::TypeError, /Expected Types::STRING, received (Integer|Fixnum) for field greeting/)
+        expect { SpecNamespace::Hello.new(:greeting => 3) }.to raise_error(Thrift::TypeError, "Expected Types::STRING, received Integer for field greeting")
       ensure
         Thrift.type_checking = false
       end
@@ -238,7 +238,7 @@
       Thrift.type_checking = true
       begin
         hello = SpecNamespace::Hello.new
-        expect { hello.greeting = 3 }.to raise_error(Thrift::TypeError, /Expected Types::STRING, received (Integer|Fixnum) for field greeting/)
+        expect { hello.greeting = 3 }.to raise_error(Thrift::TypeError, "Expected Types::STRING, received Integer for field greeting")
       ensure
         Thrift.type_checking = false
       end
diff --git a/lib/rb/spec/types_spec.rb b/lib/rb/spec/types_spec.rb
index d595ab5..a385367 100644
--- a/lib/rb/spec/types_spec.rb
+++ b/lib/rb/spec/types_spec.rb
@@ -100,9 +100,9 @@
     end
 
     it "should give the Thrift::TypeError a readable message" do
-      msg = /Expected Types::STRING, received (Integer|Fixnum) for field foo/
+      msg = "Expected Types::STRING, received Integer for field foo"
       expect { Thrift.check_type(3, {:type => Thrift::Types::STRING}, :foo) }.to raise_error(Thrift::TypeError, msg)
-      msg = /Expected Types::STRING, received (Integer|Fixnum) for field foo.element/
+      msg = "Expected Types::STRING, received Integer for field foo.element"
       field = {:type => Thrift::Types::LIST, :element => {:type => Thrift::Types::STRING}}
       expect { Thrift.check_type([3], field, :foo) }.to raise_error(Thrift::TypeError, msg)
       msg = "Expected Types::I32, received NilClass for field foo.element.key"
diff --git a/lib/rb/thrift.gemspec b/lib/rb/thrift.gemspec
index 7e1bb33..d763bad 100644
--- a/lib/rb/thrift.gemspec
+++ b/lib/rb/thrift.gemspec
@@ -12,6 +12,8 @@
   s.license     = 'Apache-2.0'
   s.extensions  = ['ext/extconf.rb']
 
+  s.required_ruby_version = '>= 2.4.0'
+
   s.rdoc_options  = %w[--line-numbers --inline-source --title Thrift --main README]
 
   dir = File.expand_path(File.dirname(__FILE__))