rails · dhh · Apr 17, 2026 · Apr 14, 2026 · Apr 14, 2026 · Apr 10, 2026
diff --git a/Gemfile.lock b/Gemfile.lock
@@ -115,7 +115,8 @@ GEM
     marcel (1.0.4)
     mini_mime (1.1.5)
     mini_portile2 (2.8.9)
-    minitest (5.25.5)
+    minitest (5.27.0)
+    minitest-mock (5.27.0)
     net-imap (0.5.9)
       date
       net-protocol
@@ -207,6 +208,7 @@ PLATFORMS
 
 DEPENDENCIES
   debug
+  minitest-mock
   propshaft!
   rails (>= 7.0.1)
   rake

diff --git a/lib/propshaft/asset.rb b/lib/propshaft/asset.rb
@@ -5,6 +5,8 @@
 class Propshaft::Asset
   attr_reader :path, :logical_path, :load_path
 
+  CONTENT_TYPES_WITH_UTF8_CHARSET = [ Mime::Type.lookup("text/html"), Mime::Type.lookup("text/css") ]
+
   class << self
     def extract_path_and_digest(digested_path)
       digest = digested_path[/-([0-9a-zA-Z]{7,128})\.(?!digested)([^.]|.map)+\z/, 1]
@@ -27,7 +29,15 @@ def content(encoding: "ASCII-8BIT")
   end
 
   def content_type
-    Mime::Type.lookup_by_extension(logical_path.extname.from(1))
+    @content_type ||= Mime::Type.lookup_by_extension(logical_path.extname.from(1))
+  end
+
+  def content_type_with_charset
+    if content_type.in? CONTENT_TYPES_WITH_UTF8_CHARSET
+      "#{content_type}; charset=utf-8"
+    else
+      content_type
+    end
   end
 
   def length

diff --git a/lib/propshaft/server.rb b/lib/propshaft/server.rb
@@ -23,7 +23,7 @@ def call(env)
           200,
           {
             Rack::CONTENT_LENGTH  => compiled_content.length.to_s,
-            Rack::CONTENT_TYPE    => asset.content_type.to_s,
+            Rack::CONTENT_TYPE    => asset.content_type_with_charset.to_s,
             VARY                  => "Accept-Encoding",
             Rack::ETAG            => "\"#{asset.digest}\"",
             Rack::CACHE_CONTROL   => "public, max-age=31536000, immutable"

diff --git a/test/fixtures/assets/first_path/test.html b/test/fixtures/assets/first_path/test.html
@@ -0,0 +1 @@
+<html><body>hello</body></html>
diff --git a/test/propshaft/asset_test.rb b/test/propshaft/asset_test.rb
@@ -19,6 +19,13 @@ class Propshaft::AssetTest < ActiveSupport::TestCase
     assert_equal "text/css", find_asset("another.css").content_type.to_s
   end
 
+  test "content type with charset" do
+    assert_equal "text/plain", find_asset("one.txt").content_type_with_charset.to_s
+    assert_equal "text/javascript", find_asset("again.js").content_type_with_charset.to_s
+    assert_equal "text/css; charset=utf-8", find_asset("another.css").content_type_with_charset.to_s
+    assert_equal "text/html; charset=utf-8", find_asset("test.html").content_type_with_charset.to_s
+  end
+
   test "length" do
     assert_equal 19, find_asset("one.txt").length
   end

diff --git a/test/propshaft/server_test.rb b/test/propshaft/server_test.rb
@@ -47,7 +47,7 @@ def call(env)
 
     assert_equal 200, last_response.status
     assert_equal last_response.body.bytesize.to_s, last_response.headers['content-length']
-    assert_equal "text/css", last_response.headers['content-type']
+    assert_equal "text/css; charset=utf-8", last_response.headers['content-type']
     assert_equal "Accept-Encoding", last_response.headers['vary']
     assert_equal "\"#{asset.digest}\"", last_response.headers['etag']
     assert_equal "public, max-age=31536000, immutable", last_response.headers['cache-control']
@@ -67,6 +67,22 @@ def call(env)
     assert_equal 200, last_response.status
   end
 
+  test "serve an HTML file with charset" do
+    asset = @assembly.load_path.find("test.html")
+    get "/assets/#{asset.digested_path}"
+
+    assert_equal 200, last_response.status
+    assert_equal "text/html; charset=utf-8", last_response.headers['content-type']
+  end
+
+  test "serve a JS file without charset" do
+    asset = @assembly.load_path.find("again.js")
+    get "/assets/#{asset.digested_path}"
+
+    assert_equal 200, last_response.status
+    assert_equal "text/javascript", last_response.headers['content-type']
+  end
+
   test "not found" do
     get "/assets/not-found.js"