diff --git a/src/ajax.js b/src/ajax.js
index add3b373..570285af 100644
--- a/src/ajax.js
+++ b/src/ajax.js
@@ -604,7 +604,7 @@ jQuery.extend({
 		s.dataTypes = jQuery.trim( s.dataType || "*" ).toLowerCase().split( rspacesAjax );
 
 		// Determine if a cross-domain request is in order
-		if ( !s.crossDomain ) {
+		if ( s.crossDomain == null ) {
 			parts = rurl.exec( s.url.toLowerCase() );
 			s.crossDomain = !!( parts &&
 				( parts[ 1 ] != ajaxLocParts[ 1 ] || parts[ 2 ] != ajaxLocParts[ 2 ] ||