diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0951901a..c98c9fc4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -8,19 +8,21 @@ jobs:
       matrix:
         ruby: [ '3.1', '3.2', '3.3', 'head' ]
         rails: [ '7.1', 'edge' ]
+        rubyopt: [""]
         include:
-          - ruby: '2.7'
-            rails: '6.1'
           - ruby: '3.0'
             rails: '6.1'
           - ruby: '3.1'
             rails: '7.0'
+          - ruby: '3.3'
+            rails: ['edge', '7.1']
+            rubyopt: "--enable-frozen-string-literal"
 
     env:
       RAILS_VERSION: ${{ matrix.rails }}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
@@ -29,10 +31,10 @@ jobs:
           bundler-cache: true
 
       - name: Run unit tests
-        run: bundle exec rake test:unit
+        run: bundle exec rake test:unit RUBYOPT="${{ matrix.rubyopt }}"
         timeout-minutes: 3
 
       - name: Run acceptance tests
-        run: bundle exec rake test:acceptance
+        run: bundle exec rake test:acceptance RUBYOPT="${{ matrix.rubyopt }}"
         timeout-minutes: 10
         if: ${{ matrix.rails != 'edge' && matrix.ruby != 'head' }} # Acceptance tests use `gem install rails && rails new`
diff --git a/lib/spring/json.rb b/lib/spring/json.rb
index d4d71b6e..ed09f4d5 100644
--- a/lib/spring/json.rb
+++ b/lib/spring/json.rb
@@ -13,7 +13,6 @@
 module Spring
   module JSON
     def self.load(string)
-      string.force_encoding("utf-8")
       OkJson.decode(string)
     end
 
@@ -364,7 +363,7 @@ def unquote(q)
             end
           end
           if rubydoesenc?
-            a[w] = '' << uchar
+            a[w] = +'' << uchar
             w += 1
           else
             w += ucharenc(a, w, uchar)
diff --git a/test/support/application.rb b/test/support/application.rb
index baeb0092..ed3cc3cb 100644
--- a/test/support/application.rb
+++ b/test/support/application.rb
@@ -168,7 +168,7 @@ def read_streams
       end
 
       def read_stream(stream)
-        output = ""
+        output = +""
         while IO.select([stream], [], [], 0.5) && !stream.eof?
           output << stream.readpartial(10240)
         end
diff --git a/test/unit/json_test.rb b/test/unit/json_test.rb
new file mode 100644
index 00000000..b9eecc05
--- /dev/null
+++ b/test/unit/json_test.rb
@@ -0,0 +1,12 @@
+require_relative "../helper"
+require 'spring/json'
+
+class JsonTest < ActiveSupport::TestCase
+  test 'can decode unicode characters' do
+    assert_equal({"unicode_example"=>"©"}, Spring::JSON.load('{"unicode_example": "\u00A9"}'))
+  end
+
+  test 'can encode' do
+    assert_equal('{}', Spring::JSON.dump({}))
+  end 
+end