diff --git a/APIKit/RequestType.swift b/APIKit/RequestType.swift
index 7eeedf9c..6f538416 100644
--- a/APIKit/RequestType.swift
+++ b/APIKit/RequestType.swift
@@ -16,7 +16,7 @@ public protocol RequestType {
     var baseURL: NSURL { get }
     var method: HTTPMethod { get }
     var path: String { get }
-    var parameters: [String: AnyObject] { get }
+    var parameters: [String: AnyObject?] { get }
 
     /// You can add any configurations here
     ///
@@ -45,7 +45,7 @@ public protocol RequestType {
 
 /// Default implementation of RequestType protocol
 public extension RequestType {
-    public var parameters: [String: AnyObject] {
+    public var parameters: [String: AnyObject?] {
         return [:]
     }
 
@@ -78,15 +78,16 @@ public extension RequestType {
         }
 
         let URLRequest = NSMutableURLRequest()
-
+        let paramObject = parametersToAnyObject(parameters)
+        
         switch method {
         case .GET, .HEAD, .DELETE:
             if parameters.count > 0 {
-                components.percentEncodedQuery = URLEncodedSerialization.stringFromDictionary(parameters)
+                components.percentEncodedQuery = URLEncodedSerialization.stringFromDictionary(paramObject)
             }
         default:
             do {
-                URLRequest.HTTPBody = try requestBodyBuilder.buildBodyFromObject(parameters)
+                URLRequest.HTTPBody = try requestBodyBuilder.buildBodyFromObject(paramObject)
             } catch {
                 return .Failure(.RequestBodySerializationError(error))
             }
@@ -133,3 +134,12 @@ public extension RequestType {
         return .Success(response)
     }
 }
+
+/// Convert `var parameters: [String: AnyObject?]` (non-AnyObject) to AnyObject using NSNull
+private func parametersToAnyObject(parameters: [String: AnyObject?]) -> [String: AnyObject] {
+    var object = [String: AnyObject]()
+    for (key, value) in parameters {
+        object[key] = value ?? NSNull()
+    }
+    return object
+}
diff --git a/APIKit/URLEncodedSerialization.swift b/APIKit/URLEncodedSerialization.swift
index 503afd4a..c3f34fc3 100644
--- a/APIKit/URLEncodedSerialization.swift
+++ b/APIKit/URLEncodedSerialization.swift
@@ -62,6 +62,10 @@ public final class URLEncodedSerialization {
     
     public static func stringFromDictionary(dictionary: [String: AnyObject]) -> String {
         let pairs = dictionary.map { key, value -> String in
+            guard (value is NSNull) == false else {
+                return "\(escape(key))"
+            }
+            
             let valueAsString = (value as? String) ?? "\(value)"
             return "\(escape(key))=\(escape(valueAsString))"
         }
diff --git a/APIKitTests/RequestCreateTaskInURLSessionTests.swift b/APIKitTests/RequestCreateTaskInURLSessionTests.swift
index 0ce36f1a..71d2fd46 100644
--- a/APIKitTests/RequestCreateTaskInURLSessionTests.swift
+++ b/APIKitTests/RequestCreateTaskInURLSessionTests.swift
@@ -18,7 +18,7 @@ class RequestCreateTaskInURLSessionTest: XCTestCase {
         var baseURL: NSURL { return NSURL(string: b)! }
         var method: HTTPMethod { return m }
         var path: String { return p  }
-        var parameters: [String: AnyObject] { return params }
+        var parameters: [String: AnyObject?] { return params }
         func responseFromObject(object: AnyObject, URLResponse: NSHTTPURLResponse) -> Response? { return nil }
     }
     
diff --git a/APIKitTests/RequestTests.swift b/APIKitTests/RequestTests.swift
index 5cd34310..6ae18dad 100644
--- a/APIKitTests/RequestTests.swift
+++ b/APIKitTests/RequestTests.swift
@@ -17,9 +17,10 @@ class RequestTests: XCTestCase {
             return "/"
         }
         
-        var parameters: [String: AnyObject] {
+        var parameters: [String: AnyObject?] {
             return [
                 "q": query,
+                "dummy": nil
             ]
         }
         
@@ -35,7 +36,7 @@ class RequestTests: XCTestCase {
 
     func testJapanesesURLQueryParameterEncoding() {
         OHHTTPStubs.stubRequestsPassingTest({ request in
-            XCTAssert(request.URL?.query == "q=%E3%81%93%E3%82%93%E3%81%AB%E3%81%A1%E3%81%AF")
+            XCTAssert(request.URL?.query == "q=%E3%81%93%E3%82%93%E3%81%AB%E3%81%A1%E3%81%AF&dummy")
             return true
         }, withStubResponse: { request in
             return OHHTTPStubsResponse(data: NSData(), statusCode: 200, headers: nil)
@@ -53,7 +54,7 @@ class RequestTests: XCTestCase {
     
     func testSymbolURLQueryParameterEncoding() {
         OHHTTPStubs.stubRequestsPassingTest({ request in
-            XCTAssert(request.URL?.query == "q=%21%22%23%24%25%26%27%28%290%3D~%7C%60%7B%7D%2A%2B%3C%3E%3F_")
+            XCTAssert(request.URL?.query == "q=%21%22%23%24%25%26%27%28%290%3D~%7C%60%7B%7D%2A%2B%3C%3E%3F_&dummy")
             return true
         }, withStubResponse: { request in
             return OHHTTPStubsResponse(data: NSData(), statusCode: 200, headers: nil)