diff --git a/benchmarks/gvl_release_acquire/benchmark.rb b/benchmarks/gvl_release_acquire/benchmark.rb
index 3c368477..bf8ad256 100644
--- a/benchmarks/gvl_release_acquire/benchmark.rb
+++ b/benchmarks/gvl_release_acquire/benchmark.rb
@@ -1,7 +1,7 @@
 require_relative "../../harness/loader"
 
 run_benchmark(5) do |num_rs, ractor_args|
-  output = File.open("/dev/null", "wb")
+  output = File.open(File::NULL, "wb")
   input = File.open("/dev/zero", "rb")
   100_000.times do
     output.write(input.read(10))
diff --git a/benchmarks/knucleotide/benchmark.rb b/benchmarks/knucleotide/benchmark.rb
index cf6234b4..94bbb028 100644
--- a/benchmarks/knucleotide/benchmark.rb
+++ b/benchmarks/knucleotide/benchmark.rb
@@ -37,6 +37,13 @@ def find_seq(seq, s)
 
 class Worker
   def initialize(&block)
+    # Platforms without fork (Windows) compute the result sequentially in this process,
+    # so their timings are not comparable with the parallel ones.
+    unless Process.respond_to?(:fork)
+      @result = yield
+      return
+    end
+
     @r, @w = IO.pipe
     @p = Process.fork do
       @r.close
@@ -47,6 +54,8 @@ def initialize(&block)
   end
 
   def result
+    return @result unless @p
+
     ret = @r.read
     @r.close
     Process.wait(@p)
diff --git a/benchmarks/railsbench/benchmark.rb b/benchmarks/railsbench/benchmark.rb
index 89561d48..f89f91a3 100644
--- a/benchmarks/railsbench/benchmark.rb
+++ b/benchmarks/railsbench/benchmark.rb
@@ -8,7 +8,7 @@
 # and this app's db/seeds.rb will delete and repopulate
 # the database, so rows shouldn't accumulate.
 Dir.chdir __dir__
-use_gemfile extra_setup_cmd: "bin/rails db:migrate db:seed"
+use_gemfile extra_setup_cmd: "ruby bin/rails db:migrate db:seed" # Windows cannot run bin/rails by its shebang
 
 require_relative 'config/environment'
 
diff --git a/harness/harness-common.rb b/harness/harness-common.rb
index 8125f2e7..161140d6 100644
--- a/harness/harness-common.rb
+++ b/harness/harness-common.rb
@@ -1,10 +1,11 @@
 require 'rbconfig'
+require 'fileutils'
 require_relative '../misc/stats'
 
 # Ensure the ruby in PATH is the ruby running this, so we can safely shell out to other commands
 ruby_in_path = `ruby -e 'print RbConfig.ruby'`
 unless ruby_in_path == RbConfig.ruby
-  ENV["PATH"] = "#{File.dirname(RbConfig.ruby)}:#{ENV["PATH"]}"
+  ENV["PATH"] = "#{File.dirname(RbConfig.ruby)}#{File::PATH_SEPARATOR}#{ENV["PATH"]}"
   ENV.merge!("GEM_HOME" => nil, "GEM_PATH" => nil) # avoid installing gems to chruby-ed Ruby
 end
 
@@ -52,7 +53,7 @@ def setup_cmds(c)
 def use_gemfile(extra_setup_cmd: nil)
   # Benchmarks should normally set their current directory and then call this method.
 
-  setup_cmds(["bundle check 2> /dev/null || bundle install", extra_setup_cmd].compact)
+  setup_cmds(["bundle check 2> #{File::NULL} || bundle install", extra_setup_cmd].compact)
 
   # Need to be in the appropriate directory for this...
   require "bundler"
@@ -236,7 +237,7 @@ def write_json_file(ruby_bench_results)
   require "json"
 
   out_path = YB_OUTPUT_FILE
-  system('mkdir', '-p', File.dirname(out_path))
+  FileUtils.mkdir_p(File.dirname(out_path))
 
   # Using default path? Print where we put it.
   puts "Writing file #{out_path}" unless ENV["RESULT_JSON_PATH"]
diff --git a/harness/harness.rb b/harness/harness.rb
index 2fac8c3f..f6bd6099 100644
--- a/harness/harness.rb
+++ b/harness/harness.rb
@@ -14,7 +14,7 @@
 
 RSS_CSV_PATH = ENV['RSS_CSV_PATH'] ? File.expand_path(ENV['RSS_CSV_PATH']) : nil
 
-system('mkdir', '-p', File.dirname(OUT_CSV_PATH))
+FileUtils.mkdir_p(File.dirname(OUT_CSV_PATH))
 
 # We could include other values in this result if more become relevant
 # but for now all we want to know is if YJIT was enabled at runtime.
diff --git a/lib/benchmark_runner.rb b/lib/benchmark_runner.rb
index 38f9222e..6d050092 100644
--- a/lib/benchmark_runner.rb
+++ b/lib/benchmark_runner.rb
@@ -3,6 +3,7 @@
 require 'csv'
 require 'json'
 require 'rbconfig'
+require 'shellwords'
 require_relative 'table_formatter'
 
 # Extracted helper methods from run_benchmarks.rb for testing
@@ -116,21 +117,23 @@ def render_graph(json_path)
       GraphRenderer.render(json_path, png_path)
     end
 
-    # Checked system - error or return info if the command fails
+    # Checked system - error or return info if the command fails.
+    # An Array command with arguments runs without a shell, so Shellwords escapes never reach the program.
     def check_call(command, env: {}, raise_error: true, quiet: ENV['BENCHMARK_QUIET'] == '1')
-      puts("+ #{command}") unless quiet
+      command_str = command.is_a?(Array) ? command.shelljoin : command
+      puts("+ #{command_str}") unless quiet
 
       result = {}
 
       if quiet
-        result[:success] = system(env, command, out: File::NULL, err: File::NULL)
+        result[:success] = system(env, *command, out: File::NULL, err: File::NULL)
       else
-        result[:success] = system(env, command)
+        result[:success] = system(env, *command)
       end
       result[:status] = $?
 
       unless result[:success]
-        puts "Command #{command.inspect} failed with exit code #{result[:status].exitstatus} in directory #{Dir.pwd}" unless quiet
+        puts "Command #{command_str.inspect} failed with exit code #{result[:status].exitstatus} in directory #{Dir.pwd}" unless quiet
         raise RuntimeError.new if raise_error
       end
 
diff --git a/lib/benchmark_runner/cli.rb b/lib/benchmark_runner/cli.rb
index ed59d2d1..8c8e2ff5 100644
--- a/lib/benchmark_runner/cli.rb
+++ b/lib/benchmark_runner/cli.rb
@@ -47,7 +47,7 @@ def run
 
       # Collect ruby version descriptions for all executables upfront
       args.executables.each do |name, executable|
-        ruby_descriptions[name] = `#{executable.shelljoin} -v`.chomp
+        ruby_descriptions[name] = IO.popen([*executable, "-v"], &:read).chomp
       end
 
       # Warn if two executables look identical (same ruby -v output and same flags)
diff --git a/lib/benchmark_suite.rb b/lib/benchmark_suite.rb
index 4c22a12a..7599152a 100644
--- a/lib/benchmark_suite.rb
+++ b/lib/benchmark_suite.rb
@@ -161,15 +161,15 @@ def run_single_benchmark(script_path, result_json_path, ruby, cmd_prefix, env, b
     ENV["RESULT_JSON_PATH"] = result_json_path
 
     # Set up the benchmarking command
-    cmd = cmd_prefix + [
+    cmd = (cmd_prefix + [
       *ruby,
       "-I", benchmark_harness,
       *pre_init,
       script_path,
-    ].compact
+    ].compact).map(&:to_s)
 
     # Do the benchmarking
-    result = BenchmarkRunner.check_call(cmd.shelljoin, env: env, raise_error: false, quiet: quiet)
+    result = BenchmarkRunner.check_call(cmd, env: env, raise_error: false, quiet: quiet)
     result[:command] = cmd.shelljoin
     result
   ensure
@@ -198,10 +198,10 @@ def compute_benchmark_env(ruby)
     # like `bundle install` in a child process will not use the Ruby being benchmarked.
     # It overrides PATH to guarantee the commands of the benchmarked Ruby will be used.
     env = {}
-    ruby_path = `#{ruby.shelljoin} -e 'print RbConfig.ruby' 2> #{File::NULL}`
+    ruby_path = IO.popen([*ruby, "-e", "print RbConfig.ruby"], err: File::NULL, &:read)
 
     if ruby_path != RbConfig.ruby
-      env["PATH"] = "#{File.dirname(ruby_path)}:#{ENV["PATH"]}"
+      env["PATH"] = "#{File.dirname(ruby_path)}#{File::PATH_SEPARATOR}#{ENV["PATH"]}"
 
       # chruby sets GEM_HOME and GEM_PATH in your shell. We have to unset it in the child
       # process to avoid installing gems to the version that is running run_benchmarks.rb.