diff --git a/src/core.js b/src/core.js
index e122305ce..31d749dd1 100644
--- a/src/core.js
+++ b/src/core.js
@@ -307,8 +307,8 @@ jQuery.extend( {
 	},
 
 	isXMLDoc: function( elem ) {
-		var namespace = elem.namespaceURI,
-			docElem = ( elem.ownerDocument || elem ).documentElement;
+		var namespace = elem && elem.namespaceURI,
+			docElem = elem && ( elem.ownerDocument || elem ).documentElement;
 
 		// Assume HTML when documentElement doesn't yet exist, such as inside
 		// document fragments.
diff --git a/test/unit/core.js b/test/unit/core.js
index e24966551..6bcea95af 100644
--- a/test/unit/core.js
+++ b/test/unit/core.js
@@ -417,6 +417,16 @@ QUnit.test( "isXMLDoc - XML", function( assert ) {
 	assert.ok( jQuery.isXMLDoc( jQuery( "desc", svg )[ 0 ] ), "XML desc Element" );
 } );
 
+QUnit.test( "isXMLDoc - falsy", function( assert ) {
+	assert.expect( 5 );
+
+	assert.strictEqual( jQuery.isXMLDoc( undefined ), false, "undefined" );
+	assert.strictEqual( jQuery.isXMLDoc( null ), false, "null" );
+	assert.strictEqual( jQuery.isXMLDoc( false ), false, "false" );
+	assert.strictEqual( jQuery.isXMLDoc( 0 ), false, "0" );
+	assert.strictEqual( jQuery.isXMLDoc( "" ), false, "\"\"" );
+} );
+
 QUnit.test( "XSS via location.hash", function( assert ) {
 	var done = assert.async();
 	assert.expect( 1 );