diff --git a/test/rubygems/fixtures/prerelease_specs.4.8.gz b/test/rubygems/fixtures/prerelease_specs.4.8.gz
new file mode 100644
index 00000000000000..15d3a53b430ddc
Binary files /dev/null and b/test/rubygems/fixtures/prerelease_specs.4.8.gz differ
diff --git a/test/rubygems/fixtures/specs.4.8.gz b/test/rubygems/fixtures/specs.4.8.gz
new file mode 100644
index 00000000000000..0e98784384d309
Binary files /dev/null and b/test/rubygems/fixtures/specs.4.8.gz differ
diff --git a/test/rubygems/test_gem_source.rb b/test/rubygems/test_gem_source.rb
index 4d445f343765d6..9516a1442291ee 100644
--- a/test/rubygems/test_gem_source.rb
+++ b/test/rubygems/test_gem_source.rb
@@ -54,8 +54,8 @@ def test_dependency_resolver_set_bundler_api
   end
 
   def test_dependency_resolver_set_file_uri
-    File.write(File.join(@tempdir, "prerelease_specs.4.8.gz"), Gem::Util.gzip("\x04\x08[\x05".b))
-    File.write(File.join(@tempdir, "specs.4.8.gz"), Gem::Util.gzip("\x04\x08[\x05".b))
+    FileUtils.cp File.expand_path(File.join("fixtures", "prerelease_specs.4.8.gz"), __dir__), @tempdir
+    FileUtils.cp File.expand_path(File.join("fixtures", "specs.4.8.gz"), __dir__), @tempdir
 
     source = Gem::Source.new "file://#{@tempdir}/"