diff --git a/lib/rubygems/config_file.rb b/lib/rubygems/config_file.rb
index 7874ad0dc9a1ca..a2bcb6dfbc249b 100644
--- a/lib/rubygems/config_file.rb
+++ b/lib/rubygems/config_file.rb
@@ -522,12 +522,12 @@ def write
 
   # Return the configuration information for +key+.
   def [](key)
-    @hash[key.to_s]
+    @hash[key] || @hash[key.to_s]
   end
 
   # Set configuration option +key+ to +value+.
   def []=(key, value)
-    @hash[key.to_s] = value
+    @hash[key] = value
   end
 
   def ==(other) # :nodoc:
@@ -555,8 +555,13 @@ def self.load_with_rubygems_config_hash(yaml)
     require_relative "yaml_serializer"
 
     content = Gem::YAMLSerializer.load(yaml)
+    deep_transform_config_keys!(content)
+  end
 
-    content.transform_keys! do |k|
+  private
+
+  def self.deep_transform_config_keys!(config)
+    config.transform_keys! do |k|
       if k.match?(/\A:(.*)\Z/)
         k[1..-1].to_sym
       elsif k.include?("__") || k.match?(%r{/\Z})
@@ -570,7 +575,7 @@ def self.load_with_rubygems_config_hash(yaml)
       end
     end
 
-    content.transform_values! do |v|
+    config.transform_values! do |v|
       if v.is_a?(String)
         if v.match?(/\A:(.*)\Z/)
           v[1..-1].to_sym
@@ -583,18 +588,18 @@ def self.load_with_rubygems_config_hash(yaml)
         else
           v
         end
-      elsif v.is_a?(Hash) && v.empty?
+      elsif v.empty?
         nil
+      elsif v.is_a?(Hash)
+        deep_transform_config_keys!(v)
       else
         v
       end
     end
 
-    content
+    config
   end
 
-  private
-
   def set_config_file_name(args)
     @config_file_name = ENV["GEMRC"]
     need_config_file_name = false
diff --git a/test/rubygems/test_gem_config_file.rb b/test/rubygems/test_gem_config_file.rb
index a055f248be7526..b28dcf503e91a5 100644
--- a/test/rubygems/test_gem_config_file.rb
+++ b/test/rubygems/test_gem_config_file.rb
@@ -575,6 +575,73 @@ def test_handle_comment
     assert_equal("bar", actual[:foo])
   end
 
+  def test_s3_source
+    yaml = <<~YAML
+      ---
+      :sources:
+      - s3://bucket1/
+      - s3://bucket2/
+      - s3://bucket3/path_to_gems_dir/
+      - s3://bucket4/
+      - https://rubygems.org/
+      :s3_source:
+        :bucket1:
+          :provider: env
+        :bucket2:
+          :provider: instance_profile
+          :region: us-west-2
+        :bucket3:
+          :id: AOUEAOEU123123AOEUAO
+          :secret: aodnuhtdao/saeuhto+19283oaehu/asoeu+123h
+          :region: us-east-2
+        :bucket4:
+          :id: AOUEAOEU123123AOEUAO
+          :secret: aodnuhtdao/saeuhto+19283oaehu/asoeu+123h
+          :security_token: AQoDYXdzEJr
+          :region: us-west-1
+    YAML
+
+    File.open @temp_conf, "w" do |fp|
+      fp.puts yaml
+    end
+    util_config_file
+
+    assert_equal(["s3://bucket1/", "s3://bucket2/", "s3://bucket3/path_to_gems_dir/", "s3://bucket4/", "https://rubygems.org/"], @cfg.sources)
+    expected_config = {
+      bucket1: { provider: "env" },
+      bucket2: { provider: "instance_profile", region: "us-west-2" },
+      bucket3: { id: "AOUEAOEU123123AOEUAO", secret: "aodnuhtdao/saeuhto+19283oaehu/asoeu+123h", region: "us-east-2" },
+      bucket4: { id: "AOUEAOEU123123AOEUAO", secret: "aodnuhtdao/saeuhto+19283oaehu/asoeu+123h", security_token: "AQoDYXdzEJr", region: "us-west-1" },
+    }
+    assert_equal(expected_config, @cfg[:s3_source])
+    assert_equal(expected_config[:bucket1], @cfg[:s3_source][:bucket1])
+    assert_equal(expected_config[:bucket2], @cfg[:s3_source][:bucket2])
+    assert_equal(expected_config[:bucket3], @cfg[:s3_source][:bucket3])
+    assert_equal(expected_config[:bucket4], @cfg[:s3_source][:bucket4])
+  end
+
+  def test_s3_source_with_config_without_lookahead
+    yaml = <<~YAML
+    :sources:
+    - s3://bucket1/
+    s3_source:
+      bucket1:
+        provider: env
+    YAML
+
+    File.open @temp_conf, "w" do |fp|
+      fp.puts yaml
+    end
+    util_config_file
+
+    assert_equal(["s3://bucket1/"], @cfg.sources)
+    expected_config = {
+      "bucket1" => { "provider" => "env" },
+    }
+    assert_equal(expected_config, @cfg[:s3_source])
+    assert_equal(expected_config[:bucket1], @cfg[:s3_source][:bucket1])
+  end
+
   def util_config_file(args = @cfg_args)
     @cfg = Gem::ConfigFile.new args
   end