diff --git a/core/dir/shared/chroot.rb b/core/dir/shared/chroot.rb
index 8c0599fe3f..a8f7c10a19 100644
--- a/core/dir/shared/chroot.rb
+++ b/core/dir/shared/chroot.rb
@@ -2,7 +2,7 @@
   before :all do
     DirSpecs.create_mock_dirs
 
-    @real_root = "../" * (File.dirname(__FILE__).count('/') - 1)
+    @real_root = "../" * (__dir__.count('/') - 1)
     @ref_dir = File.join("/", File.basename(Dir["/*"].first))
   end
 
@@ -18,7 +18,7 @@
   compilations_ci = ENV["GITHUB_WORKFLOW"] == "Compilations"
 
   it "can be used to change the process' root directory" do
-    -> { Dir.send(@method, File.dirname(__FILE__)) }.should_not raise_error
+    -> { Dir.send(@method, __dir__) }.should_not raise_error
     File.should.exist?("/#{File.basename(__FILE__)}")
   end unless compilations_ci
 
diff --git a/core/dir/shared/exist.rb b/core/dir/shared/exist.rb
index 765d1b656c..2ea4f88a80 100644
--- a/core/dir/shared/exist.rb
+++ b/core/dir/shared/exist.rb
@@ -1,6 +1,6 @@
 describe :dir_exist, shared: true do
   it "returns true if the given directory exists" do
-    Dir.send(@method, File.dirname(__FILE__)).should be_true
+    Dir.send(@method, __dir__).should be_true
   end
 
   it "returns true for '.'" do
@@ -20,7 +20,7 @@
   end
 
   it "understands relative paths" do
-    Dir.send(@method, File.dirname(__FILE__) + '/../').should be_true
+    Dir.send(@method, __dir__ + '/../').should be_true
   end
 
   it "returns false if the given directory doesn't exist" do
@@ -28,7 +28,7 @@
   end
 
   it "doesn't require the name to have a trailing slash" do
-    dir = File.dirname(__FILE__)
+    dir = __dir__
     dir.sub!(/\/$/,'')
     Dir.send(@method, dir).should be_true
   end
@@ -50,7 +50,7 @@
 
   it "calls #to_path on non String arguments" do
     p = mock('path')
-    p.should_receive(:to_path).and_return(File.dirname(__FILE__))
+    p.should_receive(:to_path).and_return(__dir__)
     Dir.send(@method, p)
   end
 end
diff --git a/core/exception/equal_value_spec.rb b/core/exception/equal_value_spec.rb
index 7f2065511a..e8f3ce0f8d 100644
--- a/core/exception/equal_value_spec.rb
+++ b/core/exception/equal_value_spec.rb
@@ -22,18 +22,18 @@
 
   it "returns true if both exceptions have the same class, the same message, and the same backtrace" do
     one = TypeError.new("message")
-    one.set_backtrace [File.dirname(__FILE__)]
+    one.set_backtrace [__dir__]
     two = TypeError.new("message")
-    two.set_backtrace [File.dirname(__FILE__)]
+    two.set_backtrace [__dir__]
     one.should == two
   end
 
   it "returns false if the two exceptions inherit from Exception but have different classes" do
     one = RuntimeError.new("message")
-    one.set_backtrace [File.dirname(__FILE__)]
+    one.set_backtrace [__dir__]
     one.should be_kind_of(Exception)
     two = TypeError.new("message")
-    two.set_backtrace [File.dirname(__FILE__)]
+    two.set_backtrace [__dir__]
     two.should be_kind_of(Exception)
     one.should_not == two
   end
@@ -52,7 +52,7 @@
 
   it "returns false if the two exceptions differ only in their backtrace" do
     one = RuntimeError.new("message")
-    one.set_backtrace [File.dirname(__FILE__)]
+    one.set_backtrace [__dir__]
     two = RuntimeError.new("message")
     two.set_backtrace nil
     one.should_not == two
@@ -60,9 +60,9 @@
 
   it "returns false if the two exceptions differ only in their message" do
     one = RuntimeError.new("message")
-    one.set_backtrace [File.dirname(__FILE__)]
+    one.set_backtrace [__dir__]
     two = RuntimeError.new("message2")
-    two.set_backtrace [File.dirname(__FILE__)]
+    two.set_backtrace [__dir__]
     one.should_not == two
   end
 end
diff --git a/core/file/absolute_path_spec.rb b/core/file/absolute_path_spec.rb
index e35c80ec3c..315eead34f 100644
--- a/core/file/absolute_path_spec.rb
+++ b/core/file/absolute_path_spec.rb
@@ -85,7 +85,7 @@
   end
 
   it "accepts a second argument of a directory from which to resolve the path" do
-    File.absolute_path(__FILE__, File.dirname(__FILE__)).should == @abs
+    File.absolute_path(__FILE__, __dir__).should == @abs
   end
 
   it "calls #to_path on its argument" do
diff --git a/core/io/eof_spec.rb b/core/io/eof_spec.rb
index 315345d942..b4850df437 100644
--- a/core/io/eof_spec.rb
+++ b/core/io/eof_spec.rb
@@ -76,7 +76,7 @@
   end
 
   it "returns true on one-byte stream after single-byte read" do
-    File.open(File.dirname(__FILE__) + '/fixtures/one_byte.txt') { |one_byte|
+    File.open(__dir__ + '/fixtures/one_byte.txt') { |one_byte|
       one_byte.read(1)
       one_byte.should.eof?
     }
diff --git a/core/kernel/require_relative_spec.rb b/core/kernel/require_relative_spec.rb
index 5999855de6..6188d13a4e 100644
--- a/core/kernel/require_relative_spec.rb
+++ b/core/kernel/require_relative_spec.rb
@@ -5,9 +5,9 @@
   before :each do
     CodeLoadingSpecs.spec_setup
     @dir = "../../fixtures/code"
-    @abs_dir = File.realpath(@dir, File.dirname(__FILE__))
+    @abs_dir = File.realpath(@dir, __dir__)
     @path = "#{@dir}/load_fixture.rb"
-    @abs_path = File.realpath(@path, File.dirname(__FILE__))
+    @abs_path = File.realpath(@path, __dir__)
   end
 
   after :each do
@@ -92,7 +92,7 @@
 
   it "raises a LoadError that includes the missing path" do
     missing_path = "#{@dir}/nonexistent.rb"
-    expanded_missing_path = File.expand_path(missing_path, File.dirname(__FILE__))
+    expanded_missing_path = File.expand_path(missing_path, __dir__)
     -> { require_relative(missing_path) }.should raise_error(LoadError) { |e|
       e.message.should include(expanded_missing_path)
       e.path.should == expanded_missing_path
@@ -277,7 +277,7 @@
 describe "Kernel#require_relative with an absolute path" do
   before :each do
     CodeLoadingSpecs.spec_setup
-    @dir = File.expand_path "../../fixtures/code", File.dirname(__FILE__)
+    @dir = File.expand_path "../../fixtures/code", __dir__
     @abs_dir = @dir
     @path = File.join @dir, "load_fixture.rb"
     @abs_path = @path
diff --git a/core/kernel/test_spec.rb b/core/kernel/test_spec.rb
index abb365aed2..d26dc06361 100644
--- a/core/kernel/test_spec.rb
+++ b/core/kernel/test_spec.rb
@@ -3,8 +3,8 @@
 
 describe "Kernel#test" do
   before :all do
-    @file = File.dirname(__FILE__) + '/fixtures/classes.rb'
-    @dir = File.dirname(__FILE__) + '/fixtures'
+    @file = __dir__ + '/fixtures/classes.rb'
+    @dir = __dir__ + '/fixtures'
   end
 
   it "is a private method" do
diff --git a/core/process/argv0_spec.rb b/core/process/argv0_spec.rb
index 7c2342f959..f5aba719e9 100644
--- a/core/process/argv0_spec.rb
+++ b/core/process/argv0_spec.rb
@@ -8,7 +8,7 @@
   it "is the path given as the main script and the same as __FILE__" do
     script = "fixtures/argv0.rb"
 
-    Dir.chdir(File.dirname(__FILE__)) do
+    Dir.chdir(__dir__) do
       ruby_exe(script).should == "#{script}\n#{script}\nOK"
     end
   end
diff --git a/core/process/exec_spec.rb b/core/process/exec_spec.rb
index deb8913b6b..2fa8b08975 100644
--- a/core/process/exec_spec.rb
+++ b/core/process/exec_spec.rb
@@ -30,7 +30,7 @@
   end
 
   it "raises Errno::EACCES when passed a directory" do
-    -> { Process.exec File.dirname(__FILE__) }.should raise_error(Errno::EACCES)
+    -> { Process.exec __dir__ }.should raise_error(Errno::EACCES)
   end
 
   it "runs the specified command, replacing current process" do
diff --git a/core/process/spawn_spec.rb b/core/process/spawn_spec.rb
index c8a58c4d04..283a7f033d 100644
--- a/core/process/spawn_spec.rb
+++ b/core/process/spawn_spec.rb
@@ -714,7 +714,7 @@ def child_pids(pid)
   end
 
   it "raises an Errno::EACCES or Errno::EISDIR when passed a directory" do
-    -> { Process.spawn File.dirname(__FILE__) }.should raise_error(SystemCallError) { |e|
+    -> { Process.spawn __dir__ }.should raise_error(SystemCallError) { |e|
       [Errno::EACCES, Errno::EISDIR].should include(e.class)
     }
   end
diff --git a/core/thread/backtrace/location/path_spec.rb b/core/thread/backtrace/location/path_spec.rb
index 7863c055d3..75f76833a9 100644
--- a/core/thread/backtrace/location/path_spec.rb
+++ b/core/thread/backtrace/location/path_spec.rb
@@ -41,7 +41,7 @@
       context 'when using a relative script path' do
         it 'returns a path relative to the working directory' do
           path      = 'fixtures/main.rb'
-          directory = File.dirname(__FILE__)
+          directory = __dir__
           Dir.chdir(directory) {
             ruby_exe(path)
           }.should == path
diff --git a/language/predefined_spec.rb b/language/predefined_spec.rb
index 6f779b55f5..fe865cc325 100644
--- a/language/predefined_spec.rb
+++ b/language/predefined_spec.rb
@@ -1037,7 +1037,7 @@ def obj.foo2; yield; end
 
   it "is the path given as the main script and the same as __FILE__" do
     script = "fixtures/dollar_zero.rb"
-    Dir.chdir(File.dirname(__FILE__)) do
+    Dir.chdir(__dir__) do
       ruby_exe(script).should == "#{script}\n#{script}\nOK"
     end
   end
diff --git a/library/net/ftp/shared/getbinaryfile.rb b/library/net/ftp/shared/getbinaryfile.rb
index 71f226089d..ceec8e7cd5 100644
--- a/library/net/ftp/shared/getbinaryfile.rb
+++ b/library/net/ftp/shared/getbinaryfile.rb
@@ -1,6 +1,6 @@
 describe :net_ftp_getbinaryfile, shared: true do
   before :each do
-    @fixture_file = File.dirname(__FILE__) + "/../fixtures/getbinaryfile"
+    @fixture_file = __dir__ + "/../fixtures/getbinaryfile"
     @tmp_file = tmp("getbinaryfile")
 
     @server = NetFTPSpecs::DummyFTP.new
diff --git a/library/net/ftp/shared/putbinaryfile.rb b/library/net/ftp/shared/putbinaryfile.rb
index 7dddcbc26b..45f53adc2a 100644
--- a/library/net/ftp/shared/putbinaryfile.rb
+++ b/library/net/ftp/shared/putbinaryfile.rb
@@ -3,7 +3,7 @@
     @server = NetFTPSpecs::DummyFTP.new
     @server.serve_once
 
-    @local_fixture_file  = File.dirname(__FILE__) + "/../fixtures/putbinaryfile"
+    @local_fixture_file  = __dir__ + "/../fixtures/putbinaryfile"
     @remote_tmp_file = tmp("binaryfile", false)
 
     @ftp = Net::FTP.new
diff --git a/library/net/ftp/shared/puttextfile.rb b/library/net/ftp/shared/puttextfile.rb
index 50e8de28e6..3836e954b8 100644
--- a/library/net/ftp/shared/puttextfile.rb
+++ b/library/net/ftp/shared/puttextfile.rb
@@ -3,7 +3,7 @@
     @server = NetFTPSpecs::DummyFTP.new
     @server.serve_once
 
-    @local_fixture_file  = File.dirname(__FILE__) + "/../fixtures/puttextfile"
+    @local_fixture_file  = __dir__ + "/../fixtures/puttextfile"
     @remote_tmp_file = tmp("textfile", false)
 
     @ftp = Net::FTP.new
diff --git a/library/net/ftp/storbinary_spec.rb b/library/net/ftp/storbinary_spec.rb
index 64c9090760..6f73344612 100644
--- a/library/net/ftp/storbinary_spec.rb
+++ b/library/net/ftp/storbinary_spec.rb
@@ -9,7 +9,7 @@
       @server = NetFTPSpecs::DummyFTP.new
       @server.serve_once
 
-      @local_fixture_file  = File.dirname(__FILE__) + "/fixtures/putbinaryfile"
+      @local_fixture_file  = __dir__ + "/fixtures/putbinaryfile"
       @tmp_file = tmp("binaryfile", false)
 
       @ftp = Net::FTP.new
diff --git a/library/net/ftp/storlines_spec.rb b/library/net/ftp/storlines_spec.rb
index a4bb7af799..32b9448732 100644
--- a/library/net/ftp/storlines_spec.rb
+++ b/library/net/ftp/storlines_spec.rb
@@ -9,7 +9,7 @@
       @server = NetFTPSpecs::DummyFTP.new
       @server.serve_once
 
-      @local_fixture_file  = File.dirname(__FILE__) + "/fixtures/puttextfile"
+      @local_fixture_file  = __dir__ + "/fixtures/puttextfile"
       @tmp_file = tmp("textfile", false)
 
       @ftp = Net::FTP.new
diff --git a/library/yaml/fixtures/common.rb b/library/yaml/fixtures/common.rb
index f7fb4037e7..895213b844 100644
--- a/library/yaml/fixtures/common.rb
+++ b/library/yaml/fixtures/common.rb
@@ -1,4 +1,4 @@
 require 'yaml'
 
 $test_file = tmp("yaml_test_file")
-$test_parse_file = File.dirname(__FILE__) + "/test_yaml.yml"
+$test_parse_file = __dir__ + "/test_yaml.yml"
diff --git a/optional/capi/object_spec.rb b/optional/capi/object_spec.rb
index 9efc892202..6ee6d65680 100644
--- a/optional/capi/object_spec.rb
+++ b/optional/capi/object_spec.rb
@@ -219,7 +219,7 @@ def six(a, b, *c, &d); end
     end
 
     it "requires a ruby file" do
-      $:.unshift File.dirname(__FILE__)
+      $:.unshift __dir__
       @o.rb_require()
       $foo.should == 7
     end
diff --git a/spec_helper.rb b/spec_helper.rb
index 3404521c03..af1c385878 100644
--- a/spec_helper.rb
+++ b/spec_helper.rb
@@ -1,5 +1,5 @@
 use_realpath = File.respond_to?(:realpath)
-root = File.dirname(__FILE__)
+root = __dir__
 dir = "fixtures/code"
 CODE_LOADING_DIR = use_realpath ? File.realpath(dir, root) : File.expand_path(dir, root)