diff --git a/src/ajax/jsonp.js b/src/ajax/jsonp.js
index 6b0f95d..05229c7 100644
--- a/src/ajax/jsonp.js
+++ b/src/ajax/jsonp.js
@@ -52,8 +52,21 @@ jQuery.ajaxPrefilter( "json jsonp", function( s, originalSettings, jqXHR ) {
 
 		// Clean-up function
 		jqXHR.always(function() {
-			// Set callback back to previous value
-			window[ jsonpCallback ] = previous;
+			// HACK workaround for bug #8744
+			// if the jsonp request timed out, we need to keep the callback
+			// function alive, as it may be fired by some browser (IE9, FF)
+			// at a later time. However, since we encountered already the
+			// timeout, we replace it by an empty dummy function.
+			// This is VERY UGLY so beware!
+			if ( responseContainer === undefined ) {
+				window[ jsonpCallback ] = function () {
+					return;
+				};
+			}
+			else {
+				// Set callback back to previous value
+				window[ jsonpCallback ] = previous;
+			} 
 			// Call if it was a function and we have a response
 			if ( responseContainer && jQuery.isFunction( previous ) ) {
 				window[ jsonpCallback ]( responseContainer[ 0 ] );