diff --git a/lib/rubygems.rb b/lib/rubygems.rb
index e35d05af9b..2b52cde0a7 100644
--- a/lib/rubygems.rb
+++ b/lib/rubygems.rb
@@ -792,21 +792,18 @@ An Array (#{env.inspect}) was passed in from #{caller[3]}
   end
 
   ##
-  # Open a file with given flags. It requires special logic on Windows, like
-  # protecting access with flock
+  # Open a file with given flags
 
   def self.open_file(path, flags, &block)
-    if !java_platform? && win_platform?
-      open_file_with_flock(path, flags, &block)
-    else
-      open_file_without_flock(path, flags, &block)
-    end
+    File.open(path, flags, &block)
   end
 
   ##
   # Open a file with given flags, and protect access with flock
 
-  def self.open_file_with_flock(path, flags, &block)
+  def self.open_file_with_flock(path, &block)
+    flags = File.exist?(path) ? "r+" : "a+"
+
     File.open(path, flags) do |io|
       begin
         io.flock(File::LOCK_EX)
@@ -817,7 +814,7 @@ An Array (#{env.inspect}) was passed in from #{caller[3]}
       if Thread.main != Thread.current
         raise
       else
-        open_file_without_flock(path, flags, &block)
+        open_file(path, flags, &block)
       end
     end
   end
@@ -1318,10 +1315,6 @@ An Array (#{env.inspect}) was passed in from #{caller[3]}
 
     private
 
-    def open_file_without_flock(path, flags, &block)
-      File.open(path, flags, &block)
-    end
-
     def already_loaded?(file)
       $LOADED_FEATURES.any? do |feature_path|
         feature_path.end_with?(file) && default_gem_load_paths.any? {|load_path_entry| feature_path == "#{load_path_entry}/#{file}" }
diff --git a/lib/rubygems/installer.rb b/lib/rubygems/installer.rb
index f637e7b604..3705174ff0 100644
--- a/lib/rubygems/installer.rb
+++ b/lib/rubygems/installer.rb
@@ -222,7 +222,7 @@ class Gem::Installer
     ruby_executable = false
     existing = nil
 
-    Gem.open_file_with_flock generated_bin, "rb+" do |io|
+    File.open generated_bin, "rb" do |io|
       line = io.gets
       shebang = /^#!.*ruby/o
 
@@ -541,8 +541,8 @@ class Gem::Installer
     require "fileutils"
     FileUtils.rm_f bin_script_path # prior install may have been --no-wrappers
 
-    File.open bin_script_path, "wb", 0o755 do |file|
-      file.print app_script_text(filename)
+    Gem.open_file_with_flock(bin_script_path) do |file|
+      file.write app_script_text(filename)
       file.chmod(options[:prog_mode] || 0o755)
     end