diff --git a/test/fileutils/test_fileutils.rb b/test/fileutils/test_fileutils.rb
index 1a93c01..eafb131 100644
--- a/test/fileutils/test_fileutils.rb
+++ b/test/fileutils/test_fileutils.rb
@@ -1049,7 +1049,7 @@ def test_ln_s_relative_to_symlinked_directory
     lnfname = File.join(dest, 'zsh')
 
     if /mingw|mswin/ =~ RUBY_PLATFORM
-      unless /<SYMLINKD>/ =~ IO.popen({"DIRCMD"=>nil}, "dir zsh", chdir: File.dirname(dest), &:read)
+      unless /<SYMLINKD>/ =~ IO.popen({"DIRCMD"=>nil}, "dir zsh", "rb", chdir: File.dirname(dest), &:read)
         omit "[Bug #22338]"
       end
     end