diff --git a/src/ajax/jsonp.js b/src/ajax/jsonp.js
index 9965b2230..4340d9acc 100644
--- a/src/ajax/jsonp.js
+++ b/src/ajax/jsonp.js
@@ -1,14 +1,15 @@
 (function( jQuery ) {
 
-var jsc = jQuery.now(),
-	jsre = /(\=)\?(&|$)|\?\?/i,
-	jscallbacks = [];
+var oldCallbacks = [],
+	rquestion = /\?/,
+	rjsonp = /(=)\?(?=&|$)|\?\?/,
+	nonce = jQuery.now();
 
 // Default jsonp settings
 jQuery.ajaxSetup({
 	jsonp: "callback",
 	jsonpCallback: function() {
-		var callback = jscallbacks.pop() || ( jQuery.expando + "_" + ( jsc++ ) );
+		var callback = oldCallbacks.pop() || ( jQuery.expando + "_" + ( nonce++ ) );
 		this[ callback ] = true;
 		return callback;
 	}
@@ -17,62 +18,38 @@ jQuery.ajaxSetup({
 // Detect, normalize options and install callbacks for jsonp requests
 jQuery.ajaxPrefilter( "json jsonp", function( s, originalSettings, jqXHR ) {
 
-	var inspectData = ( typeof s.data === "string" ) && /^application\/x\-www\-form\-urlencoded/.test( s.contentType );
+	var callbackName, overwritten, responseContainer,
+		data = s.data,
+		url = s.url,
+		hasCallback = s.jsonp !== false,
+		replaceInUrl = hasCallback && rjsonp.test( url ),
+		replaceInData = hasCallback && typeof data === "string" &&
+			!( s.contentType || "" ).indexOf("application/x-www-form-urlencoded") &&
+			rjsonp.test( data );
 
-	if ( s.dataTypes[ 0 ] === "jsonp" ||
-		s.jsonp !== false && ( jsre.test( s.url ) ||
-				inspectData && jsre.test( s.data ) ) ) {
+	// Handle iff the expected data type is "jsonp" or we have a parameter to set
+	if ( s.dataTypes[ 0 ] === "jsonp" || hasCallback &&
+		( replaceInUrl || replaceInData ) ) {
 
-		var responseContainer,
-			jsonpCallback = s.jsonpCallback =
-				jQuery.isFunction( s.jsonpCallback ) ? s.jsonpCallback() : s.jsonpCallback,
-			previous = window[ jsonpCallback ],
-			url = s.url,
-			data = s.data,
-			replace = "$1" + jsonpCallback + "$2";
+		// Get callback name, remembering preexisting value associated with it
+		callbackName = s.jsonpCallback = jQuery.isFunction( s.jsonpCallback ) ?
+			s.jsonpCallback() :
+			s.jsonpCallback;
+		overwritten = window[ callbackName ];
 
-		if ( s.jsonp !== false ) {
-			url = url.replace( jsre, replace );
-			if ( s.url === url ) {
-				if ( inspectData ) {
-					data = data.replace( jsre, replace );
-				}
-				if ( s.data === data ) {
-					// Add callback manually
-					url += (/\?/.test( url ) ? "&" : "?") + s.jsonp + "=" + jsonpCallback;
-				}
-			}
+		// Insert callback into url or form data
+		if ( replaceInUrl ) {
+			s.url = url.replace( rjsonp, "$1" + callbackName );
+		} else if ( replaceInData ) {
+			s.data = data.replace( rjsonp,"$1" + callbackName );
+		} else if ( hasCallback ) {
+			s.url += ( rquestion.test( url ) ? "&" : "?" ) + s.jsonp + "=" + callbackName;
 		}
 
-		s.url = url;
-		s.data = data;
-
-		// Install callback
-		window[ jsonpCallback ] = function( response ) {
-			responseContainer = [ response ];
-		};
-
-		// Clean-up function
-		jqXHR.always(function() {
-			// Set callback back to previous value
-			window[ jsonpCallback ] = previous;
-			// Save back as free
-			if ( s[ jsonpCallback ] ) {
-				// make sure that re-using the options doesn't screw things around
-				s.jsonpCallback = originalSettings.jsonpCallback;
-				// save the callback name for future use
-				jscallbacks.push( jsonpCallback );
-			}
-			// Call if it was a function and we have a response
-			if ( responseContainer && jQuery.isFunction( previous ) ) {
-				window[ jsonpCallback ]( responseContainer[ 0 ] );
-			}
-		});
-
 		// Use data converter to retrieve json after script execution
 		s.converters["script json"] = function() {
 			if ( !responseContainer ) {
-				jQuery.error( jsonpCallback + " was not called" );
+				jQuery.error( callbackName + " was not called" );
 			}
 			return responseContainer[ 0 ];
 		};
@@ -80,6 +57,33 @@ jQuery.ajaxPrefilter( "json jsonp", function( s, originalSettings, jqXHR ) {
 		// force json dataType
 		s.dataTypes[ 0 ] = "json";
 
+		// Install callback
+		window[ callbackName ] = function() {
+			responseContainer = arguments;
+		};
+
+		// Clean-up function (fires after converters)
+		jqXHR.always(function() {
+			// Restore preexisting value
+			window[ callbackName ] = overwritten;
+
+			// Save back as free
+			if ( s[ callbackName ] ) {
+				// make sure that re-using the options doesn't screw things around
+				s.jsonpCallback = originalSettings.jsonpCallback;
+
+				// save the callback name for future use
+				oldCallbacks.push( callbackName );
+			}
+
+			// Call if it was a function and we have a response
+			if ( responseContainer && jQuery.isFunction( overwritten ) ) {
+				overwritten( responseContainer[ 0 ] );
+			}
+
+			responseContainer = overwritten = undefined;
+		});
+
 		// Delegate to script
 		return "script";
 	}