diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4fe4f33cc..c35443079 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@ Get upgrade notes from Sprockets 3.x to 4.x at https://github.com/rails/sprocket
 
 - Add support for Rack 3.0. Headers set by sprockets will now be lower case. [#758](https://github.com/rails/sprockets/pull/758)
 - Make `Sprockets::Utils.module_include` thread safe on JRuby. [#759](https://github.com/rails/sprockets/pull/759)
+- Improve reproducibility. [#761](https://github.com/rails/sprockets/pull/761)
 
 ## 4.1.0
 
diff --git a/lib/sprockets/manifest.rb b/lib/sprockets/manifest.rb
index 8eda60e4e..38bcffd79 100644
--- a/lib/sprockets/manifest.rb
+++ b/lib/sprockets/manifest.rb
@@ -4,8 +4,6 @@
 
 require 'concurrent'
 
-require 'sprockets/manifest_utils'
-
 module Sprockets
   # The Manifest logs the contents of assets compiled to a single directory. It
   # records basic attributes about the asset for fast lookup without having to
@@ -17,7 +15,6 @@ module Sprockets
   # that don't have sprockets loaded. See `#assets` and `#files` for more
   # information about the structure.
   class Manifest
-    include ManifestUtils
 
     attr_reader :environment
 
@@ -51,19 +48,14 @@ def initialize(*args)
       # Default dir to the directory of the filename
       @directory ||= File.dirname(@filename) if @filename
 
-      # If directory is given w/o filename, pick a random manifest location
-      if @directory && @filename.nil?
-        @filename = find_directory_manifest(@directory, logger)
-      end
-
-      unless @directory && @filename
+      unless @directory
         raise ArgumentError, "manifest requires output filename"
       end
 
       data = {}
 
       begin
-        if File.exist?(@filename)
+        if !@filename.nil? && File.exist?(@filename)
           data = json_decode(File.read(@filename))
         end
       rescue JSON::ParserError => e
@@ -172,7 +164,7 @@ def compile(*args)
       end
 
       assets_to_export.each do |asset|
-        mtime = Time.now.iso8601
+        mtime = Time.at(1).utc.to_datetime.iso8601 # for reproducibility
         files[asset.digest_path] = {
           'logical_path' => asset.logical_path,
           'mtime'        => mtime,
@@ -277,6 +269,13 @@ def clobber
     # Persist manifest back to FS
     def save
       data = json_encode(@data)
+
+      # If directory is given w/o filename, use reproducible manifest location
+      if @directory && @filename.nil?
+        etag = DigestUtils.pack_hexdigest(DigestUtils.digest(@data))
+        @filename = File.join(@directory, ".sprockets-manifest-#{etag}.json")
+      end
+
       FileUtils.mkdir_p File.dirname(@filename)
       PathUtils.atomic_write(@filename) do |f|
         f.write(data)
diff --git a/lib/sprockets/manifest_utils.rb b/lib/sprockets/manifest_utils.rb
deleted file mode 100644
index 703fa1f6e..000000000
--- a/lib/sprockets/manifest_utils.rb
+++ /dev/null
@@ -1,48 +0,0 @@
-# frozen_string_literal: true
-require 'securerandom'
-require 'logger'
-
-module Sprockets
-  # Public: Manifest utilities.
-  module ManifestUtils
-    extend self
-
-    MANIFEST_RE = /^\.sprockets-manifest-[0-9a-f]{32}.json$/
-
-    # Public: Generate a new random manifest path.
-    #
-    # Manifests are not intended to be accessed publicly, but typically live
-    # alongside public assets for convenience. To avoid being served, the
-    # filename is prefixed with a "." which is usually hidden by web servers
-    # like Apache. To help in other environments that may not control this,
-    # a random hex string is appended to the filename to prevent people from
-    # guessing the location. If directory indexes are enabled on the server,
-    # all bets are off.
-    #
-    # Return String path.
-    def generate_manifest_path
-      ".sprockets-manifest-#{SecureRandom.hex(16)}.json"
-    end
-
-    # Public: Find or pick a new manifest filename for target build directory.
-    #
-    # dirname - String dirname
-    #
-    # Examples
-    #
-    #     find_directory_manifest("/app/public/assets")
-    #     # => "/app/public/assets/.sprockets-manifest-abc123.json"
-    #
-    # Returns String filename.
-    def find_directory_manifest(dirname, logger = Logger.new($stderr))
-      entries = File.directory?(dirname) ? Dir.entries(dirname) : []
-      manifest_entries = entries.select { |e| e =~ MANIFEST_RE }
-      if manifest_entries.length > 1
-        manifest_entries.sort!
-        logger.warn("Found multiple manifests: #{manifest_entries}. Choosing the first alphabetically: #{manifest_entries.first}")
-      end
-      entry = manifest_entries.first || generate_manifest_path
-      File.join(dirname, entry)
-    end
-  end
-end
diff --git a/lib/sprockets/utils/gzip.rb b/lib/sprockets/utils/gzip.rb
index 3fd5228a6..0010de1da 100644
--- a/lib/sprockets/utils/gzip.rb
+++ b/lib/sprockets/utils/gzip.rb
@@ -12,7 +12,7 @@ class Gzip
       module ZlibArchiver
         def self.call(file, source, mtime)
           gz = Zlib::GzipWriter.new(file, Zlib::BEST_COMPRESSION)
-          gz.mtime = mtime
+          gz.mtime = 1 # for reproducibility
           gz.write(source)
           gz.close
 
diff --git a/test/test_manifest.rb b/test/test_manifest.rb
index c8f554292..f9d4a92a6 100644
--- a/test/test_manifest.rb
+++ b/test/test_manifest.rb
@@ -50,11 +50,10 @@ def teardown
     assert_equal filename, manifest.path
   end
 
-  test "specify manifest directory yields random .sprockets-manifest-*.json" do
+  test "specify manifest directory reproducible .sprockets-manifest-*.json" do
     manifest = Sprockets::Manifest.new(@env, @dir)
 
     assert_equal @dir, manifest.directory
-    assert_match(/^\.sprockets-manifest-[a-f0-9]{32}.json/, File.basename(manifest.filename))
 
     manifest.save
     assert_match(/^\.sprockets-manifest-[a-f0-9]{32}.json/, File.basename(manifest.filename))
diff --git a/test/test_manifest_utils.rb b/test/test_manifest_utils.rb
deleted file mode 100644
index 02a1755bb..000000000
--- a/test/test_manifest_utils.rb
+++ /dev/null
@@ -1,37 +0,0 @@
-# frozen_string_literal: true
-require 'minitest/autorun'
-require 'sprockets/manifest_utils'
-require 'logger'
-
-class TestManifestUtils < MiniTest::Test
-  include Sprockets::ManifestUtils
-
-  def test_generate_manifest_path
-    assert_match(MANIFEST_RE, generate_manifest_path)
-  end
-
-  def test_find_directory_manifest
-    root = File.expand_path("../fixtures/manifest_utils", __FILE__)
-
-    assert_match MANIFEST_RE, File.basename(find_directory_manifest(root))
-
-    assert_equal "#{root}/default/.sprockets-manifest-f4bf345974645583d284686ddfb7625e.json",
-      find_directory_manifest("#{root}/default")
-
-  end
-
-  def test_warn_on_two
-    root = File.expand_path("../fixtures/manifest_utils", __FILE__)
-
-    assert_match MANIFEST_RE, File.basename(find_directory_manifest(root))
-
-    r, w = IO.pipe
-    logger = Logger.new(w)
-    # finds the first one alphabetically
-    assert_equal "#{root}/with_two_manifests/.sprockets-manifest-00000000000000000000000000000000.json",
-      find_directory_manifest("#{root}/with_two_manifests", logger)
-    output = r.gets
-
-    assert_match(/W, \[[^\]]+\]  WARN -- : Found multiple manifests: .+ Choosing the first alphabetically: \.sprockets-manifest-00000000000000000000000000000000\.json/, output)
-  end
-end