diff --git a/activesupport/lib/active_support/core_ext/hash/conversions.rb b/activesupport/lib/active_support/core_ext/hash/conversions.rb
index 10435975c53d..37d035ecf26f 100644
--- a/activesupport/lib/active_support/core_ext/hash/conversions.rb
+++ b/activesupport/lib/active_support/core_ext/hash/conversions.rb
@@ -221,7 +221,7 @@ def unrename_keys(params)
               case params.class.to_s
                 when "Hash"
                   params.inject({}) do |h,(k,v)|
-                    h[k.to_s.underscore.tr("-", "_")] = unrename_keys(v)
+                    h[k.to_s.tr("-", "_")] = unrename_keys(v)
                     h
                   end
                 when "Array"
diff --git a/activesupport/test/core_ext/hash_ext_test.rb b/activesupport/test/core_ext/hash_ext_test.rb
index 0edac72fe7ba..31519a1654ae 100644
--- a/activesupport/test/core_ext/hash_ext_test.rb
+++ b/activesupport/test/core_ext/hash_ext_test.rb
@@ -654,6 +654,22 @@ def test_empty_array_from_xml
     assert_equal expected_blog_hash, Hash.from_xml(blog_xml)
   end
 
+  def test_all_caps_key_from_xml
+    test_xml = <<-EOT
+      <ABC3XYZ>
+        <TEST>Lorem Ipsum</TEST>
+      </ABC3XYZ>
+    EOT
+
+    expected_hash = {
+      "ABC3XYZ" => {
+        "TEST" => "Lorem Ipsum"
+      }
+    }
+
+    assert_equal expected_hash, Hash.from_xml(test_xml)
+  end
+
   def test_empty_array_with_whitespace_from_xml
     blog_xml = <<-XML
       <blog>