diff --git a/lib/prism/ffi.rb b/lib/prism/ffi.rb
index 35b91e41b2..a0da0b6195 100644
--- a/lib/prism/ffi.rb
+++ b/lib/prism/ffi.rb
@@ -7,6 +7,10 @@
 require "rbconfig"
 require "ffi"
 
+# We want to eagerly load this file if there are Ractors so that it does not get
+# autoloaded from within a non-main Ractor.
+require "prism/serialize" if defined?(Ractor)
+
 module Prism
   module LibRubyParser # :nodoc:
     extend FFI::Library
@@ -159,6 +163,9 @@ module Prism
     class PrismString # :nodoc:
       SIZEOF = LibRubyParser.pm_string_sizeof
 
+      PLATFORM_EXPECTS_UTF8 =
+        RbConfig::CONFIG["host_os"].match?(/bccwin|cygwin|djgpp|mingw|mswin|wince|darwin/i)
+
       attr_reader :pointer, :length
 
       def initialize(pointer, length, from_string)
@@ -193,8 +200,7 @@ module Prism
         # On Windows and Mac, it's expected that filepaths will be encoded in
         # UTF-8. If they are not, we need to convert them to UTF-8 before
         # passing them into pm_string_mapped_init.
-        if RbConfig::CONFIG["host_os"].match?(/bccwin|cygwin|djgpp|mingw|mswin|wince|darwin/i) &&
-           (encoding = filepath.encoding) != Encoding::ASCII_8BIT && encoding != Encoding::UTF_8
+        if PLATFORM_EXPECTS_UTF8 && (encoding = filepath.encoding) != Encoding::ASCII_8BIT && encoding != Encoding::UTF_8
           filepath = filepath.encode(Encoding::UTF_8)
         end
 
@@ -223,7 +229,7 @@ module Prism
   private_constant :LibRubyParser
 
   # The version constant is set by reading the result of calling pm_version.
-  VERSION = LibRubyParser.pm_version.read_string
+  VERSION = LibRubyParser.pm_version.read_string.freeze
 
   class << self
     # Mirror the Prism.dump API by using the serialization API.
diff --git a/prism/extension.c b/prism/extension.c
index dca2ee67a1..1533ca7bb3 100644
--- a/prism/extension.c
+++ b/prism/extension.c
@@ -1331,6 +1331,11 @@ Init_prism(void) {
         );
     }
 
+#ifdef HAVE_RB_EXT_RACTOR_SAFE
+    // Mark this extension as Ractor-safe.
+    rb_ext_ractor_safe(true);
+#endif
+
     // Grab up references to all of the constants that we're going to need to
     // reference throughout this extension.
     rb_cPrism = rb_define_module("Prism");
diff --git a/prism/templates/lib/prism/serialize.rb.erb b/prism/templates/lib/prism/serialize.rb.erb
index 0b9e83eb0a..104b60f484 100644
--- a/prism/templates/lib/prism/serialize.rb.erb
+++ b/prism/templates/lib/prism/serialize.rb.erb
@@ -592,7 +592,7 @@ module Prism
       <%- tokens.each do |token| -%>
       <%= token.name.to_sym.inspect %>,
       <%- end -%>
-    ]
+    ].freeze
 
     private_constant :MAJOR_VERSION, :MINOR_VERSION, :PATCH_VERSION
     private_constant :ConstantPool, :FastStringIO, :Loader, :TOKEN_TYPES
diff --git a/test/prism/ractor_test.rb b/test/prism/ractor_test.rb
new file mode 100644
index 0000000000..68fc0508c8
--- /dev/null
+++ b/test/prism/ractor_test.rb
@@ -0,0 +1,77 @@
+# frozen_string_literal: true
+
+return unless defined?(Ractor)
+
+require_relative "test_helper"
+
+return if Prism::TestCase.windows?
+
+module Prism
+  class RactorTest < TestCase
+    def test_version
+      assert_match(/\A\d+\.\d+\.\d+\z/, with_ractor { Prism::VERSION })
+    end
+
+    def test_parse_file
+      assert_equal("Prism::ParseResult", with_ractor(__FILE__) { |filepath| Prism.parse_file(filepath).class })
+    end
+
+    def test_lex_file
+      assert_equal("Prism::LexResult", with_ractor(__FILE__) { |filepath| Prism.lex_file(filepath).class })
+    end
+
+    def test_parse_file_comments
+      assert_equal("Array", with_ractor(__FILE__) { |filepath| Prism.parse_file_comments(filepath).class })
+    end
+
+    def test_parse_lex_file
+      assert_equal("Prism::ParseLexResult", with_ractor(__FILE__) { |filepath| Prism.parse_lex_file(filepath).class })
+    end
+
+    def test_parse_success
+      assert_equal("true", with_ractor("1 + 1") { |source| Prism.parse_success?(source) })
+    end
+
+    def test_parse_failure
+      assert_equal("true", with_ractor("1 +") { |source| Prism.parse_failure?(source) })
+    end
+
+    def test_string_query_local
+      assert_equal("true", with_ractor("foo") { |source| StringQuery.local?(source) })
+    end
+
+    def test_string_query_constant
+      assert_equal("true", with_ractor("FOO") { |source| StringQuery.constant?(source) })
+    end
+
+    def test_string_query_method_name
+      assert_equal("true", with_ractor("foo?") { |source| StringQuery.method_name?(source) })
+    end
+
+    if !ENV["PRISM_BUILD_MINIMAL"]
+      def test_dump_file
+        result = with_ractor(__FILE__) { |filepath| Prism.dump_file(filepath) }
+        assert_operator(result, :start_with?, "PRISM")
+      end
+    end
+
+    private
+
+    # Note that this must be done in a subprocess, otherwise it can mess up
+    # CRuby's test suite.
+    def with_ractor(*arguments, &block)
+      reader, writer = IO.pipe
+
+      pid = fork do
+        reader.close
+        writer.puts(ignore_warnings { Ractor.new(*arguments, &block) }.take)
+      end
+
+      writer.close
+      result = reader.gets.chomp
+
+      Process.wait(pid)
+      result
+    end
+  end
+end
diff --git a/test/prism/result/warnings_test.rb b/test/prism/result/warnings_test.rb
index 04542dbada..4643fb134f 100644
--- a/test/prism/result/warnings_test.rb
+++ b/test/prism/result/warnings_test.rb
@@ -339,7 +339,7 @@ module Prism
       assert_warning("tap { redo; foo }", "statement not reached")
     end
 
-    if RbConfig::CONFIG["host_os"].match?(/bccwin|cygwin|djgpp|mingw|mswin|wince/i)
+    if windows?
       def test_shebang_ending_with_carriage_return
         refute_warning("#!ruby\r\np(123)\n", compare: false)
       end
diff --git a/test/prism/test_helper.rb b/test/prism/test_helper.rb
index 8a137cb636..13da37b687 100644
--- a/test/prism/test_helper.rb
+++ b/test/prism/test_helper.rb
@@ -212,6 +212,11 @@ module Prism
       yield Encoding::EUC_TW, codepoints_euc_tw
     end
 
+    # True if the current platform is Windows.
+    def self.windows?
+      RbConfig::CONFIG["host_os"].match?(/bccwin|cygwin|djgpp|mingw|mswin|wince/i)
+    end
+
     private
 
     if RUBY_ENGINE == "ruby" && RubyVM::InstructionSequence.compile("").to_a[4][:parser] != :prism