diff --git a/src/attributes/attr.js b/src/attributes/attr.js
index 4c43eb1fc..9822f3e61 100644
--- a/src/attributes/attr.js
+++ b/src/attributes/attr.js
@@ -106,12 +106,19 @@ jQuery.extend( {
 // Hooks for boolean attributes
 boolHook = {
 	set: function( elem, value, name ) {
+		var strValue = String( value );
+
 		if ( value === false ) {
 
 			// Remove boolean attributes when set to false
 			jQuery.removeAttr( elem, name );
 		} else {
-			elem.setAttribute( name, name );
+			elem.setAttribute( name,
+				name.toLowerCase() === "hidden" &&
+						strValue.toLowerCase() === "until-found" ?
+					strValue :
+					name
+			);
 		}
 		return name;
 	}
@@ -129,9 +136,13 @@ jQuery.each( jQuery.expr.match.bool.source.match( /\w+/g ), function( _i, name )
 			// Avoid an infinite loop by temporarily removing this function from the getter
 			handle = attrHandle[ lowercaseName ];
 			attrHandle[ lowercaseName ] = ret;
-			ret = getter( elem, name, isXML ) != null ?
-				lowercaseName :
-				null;
+
+			ret = getter( elem, name, isXML );
+			ret = ret == null ||
+					( lowercaseName === "hidden" && ret.toLowerCase() === "until-found" ) ?
+				ret :
+				lowercaseName;
+
 			attrHandle[ lowercaseName ] = handle;
 		}
 		return ret;
diff --git a/test/unit/attributes.js b/test/unit/attributes.js
index 34bf579b8..b2360dfc9 100644
--- a/test/unit/attributes.js
+++ b/test/unit/attributes.js
@@ -479,6 +479,24 @@ QUnit.test( "attr(String, Object)", function( assert ) {
 	assert.equal( jQuery( "#name" ).attr( "nonexisting", undefined ).attr( "nonexisting" ), undefined, ".attr('attribute', undefined) does not create attribute (trac-5571)" );
 } );
 
+QUnit.test( "attr( previously-boolean-attr, non-boolean-value)", function( assert ) {
+	assert.expect( 3 );
+
+	var div = jQuery( "<div></div>" ).appendTo( "#qunit-fixture" );
+
+	div.attr( "hidden", "foo" );
+	assert.strictEqual( div.attr( "hidden" ), "hidden",
+		"Values normalized for previously-boolean hidden attribute" );
+
+	div.attr( "hidden", "until-found" );
+	assert.strictEqual( div.attr( "hidden" ), "until-found",
+		"`until-found` value preserved for hidden attribute" );
+
+	div.attr( "hiDdeN", "uNtil-fOund" );
+	assert.strictEqual( div.attr( "hidden" ), "uNtil-fOund",
+		"`uNtil-fOund` different casing preserved" );
+} );
+
 QUnit.test( "attr(non-ASCII)", function( assert ) {
 	assert.expect( 2 );