diff --git a/src/ajax.js b/src/ajax.js
index 11eacee71..39abe9059 100644
--- a/src/ajax.js
+++ b/src/ajax.js
@@ -842,8 +842,9 @@ function ajaxConvert( s, response ) {
 	}
 
 	var dataTypes = s.dataTypes,
-		converters = s.converters,
+		converters = {},
 		i,
+		key,
 		length = dataTypes.length,
 		tmp,
 		// Current and previous dataTypes
@@ -860,6 +861,16 @@ function ajaxConvert( s, response ) {
 	// For each dataType in the chain
 	for( i = 1; i < length; i++ ) {
 
+		// Create converters map
+		// with lowercased keys
+		if ( i === 1 ) {
+			for( key in s.converters ) {
+				if( typeof key === "string" ) {
+					converters[ key.toLowerCase() ] = s.converters[ key ];
+				}
+			}
+		}
+
 		// Get the dataTypes
 		prev = current;
 		current = dataTypes[ i ];
diff --git a/test/unit/ajax.js b/test/unit/ajax.js
index 716ed9c97..9d088f3c7 100644
--- a/test/unit/ajax.js
+++ b/test/unit/ajax.js
@@ -2077,12 +2077,12 @@ test("jQuery.ajax - transitive conversions", function() {
 
 		jQuery.ajax( url("data/json.php") , {
 			converters: {
-				"json myjson": function( data ) {
+				"json myJson": function( data ) {
 					ok( true , "converter called" );
 					return data;
 				}
 			},
-			dataType: "myjson",
+			dataType: "myJson",
 			success: function() {
 				ok( true , "Transitive conversion worked" );
 				strictEqual( this.dataTypes[0] , "text" , "response was retrieved as text" );
@@ -2092,13 +2092,13 @@ test("jQuery.ajax - transitive conversions", function() {
 
 		jQuery.ajax( url("data/json.php") , {
 			converters: {
-				"json myjson": function( data ) {
+				"json myJson": function( data ) {
 					ok( true , "converter called (*)" );
 					return data;
 				}
 			},
 			contents: false, /* headers are wrong so we ignore them */
-			dataType: "* myjson",
+			dataType: "* myJson",
 			success: function() {
 				ok( true , "Transitive conversion worked (*)" );
 				strictEqual( this.dataTypes[0] , "text" , "response was retrieved as text (*)" );