Index: ajax.js
===================================================================
--- ajax.js	(revision 541)
+++ ajax.js	(working copy)
@@ -701,6 +701,7 @@
 			success: fvoid,
 			error: fvoid,
 			dataType: null,
+			contentType: "application/x-www-form-urlencoded",
 			data: null,
 			url: null
 		}, s);
@@ -736,7 +737,7 @@
 
 		// Set the correct header, if data is being sent
 		if ( s.data )
-			xml.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
+			xml.setRequestHeader("Content-Type", contentType);
 
 		// Set the If-Modified-Since header, if ifModified mode.
 		if ( s.ifModified )