diff --git a/src/ajax.js b/src/ajax.js
index 0f5f805..e5526ee 100644
--- a/src/ajax.js
+++ b/src/ajax.js
@@ -195,7 +195,17 @@ jQuery.extend({
 
 		// Build temporary JSONP function
 		if ( s.dataType == "json" && (s.data && s.data.match(jsre) || s.url.match(jsre)) ) {
-			jsonp = "jsonp" + jsc++;
+			if ( typeof s.callbackName === "string" ) {
+				// callbackName is used to request the given content with a constant URL.
+				// This enables both the browser and the server to cache the data.
+				// s.cache = false would negate the effect.
+				s.cache = true;
+
+				jsonp = "jsonp" + s.callbackName;
+				if ( window[ jsonp ] )
+					throw "callbackName " + s.callbackName + " not unique";
+			} else
+				jsonp = "jsonp" + jsc++;
 
 			// Replace the =? sequence both in the query string and the data
 			if ( s.data )
diff --git a/test/unit/ajax.js b/test/unit/ajax.js
index 0d2f071..81ae0b5 100644
--- a/test/unit/ajax.js
+++ b/test/unit/ajax.js
@@ -442,10 +442,10 @@ test("jQuery.getScript(String, Function) - no callback", function() {
 });
 
 test("jQuery.ajax() - JSONP, Local", function() {
-	expect(7);
+	expect(8);
 
 	var count = 0;
-	function plus(){ if ( ++count == 7 ) start(); }
+	function plus(){ if ( ++count == 8 ) start(); }
 
 	stop();
 
@@ -504,6 +504,20 @@ test("jQuery.ajax() - JSONP, Local", function() {
 	});
 
 	jQuery.ajax({
+		url: "data/jsonp.php",
+		dataType: "jsonp",
+		callbackName: "Test",
+		success: function(data){
+			ok( data.data, "JSON results returned (GET, specified callbackName)" );
+			plus();
+		},
+		error: function(data){
+			ok( false, "Ajax error JSON (GET, specified callbackName)" );
+			plus();
+		}
+	});
+
+	jQuery.ajax({
 		type: "POST",
 		url: "data/jsonp.php",
 		dataType: "jsonp",