diff --git a/declarations.d.ts b/declarations.d.ts
index 91eb4ca7d..1e459b3a8 100644
--- a/declarations.d.ts
+++ b/declarations.d.ts
@@ -28,6 +28,34 @@ declare var console: Console;
 declare var global;
 declare var require;
 
+//XMLHttpRequest-related
+interface FormData {
+    append(name: any, value: any, blobName?: string): void;
+}
+
+declare var FormData: {
+    prototype: FormData;
+    new (): FormData;
+}
+
+interface Blob {
+    size: number;
+    type: string;
+    msClose(): void;
+    msDetachStream(): any;
+    slice(start?: number, end?: number, contentType?: string): Blob;
+}
+
+declare var Blob: {
+    prototype: Blob;
+    new (blobParts?: any[], options?: BlobPropertyBag): Blob;
+}
+
+interface BlobPropertyBag {
+    type?: string;
+    endings?: string;
+}
+
 // Global functions
 declare function Deprecated(target: Object, key?: string | symbol, value?: any): void;
 
diff --git a/fetch/webidl.d.ts b/fetch/webidl.d.ts
index 62bae8bca..eab04ca20 100644
--- a/fetch/webidl.d.ts
+++ b/fetch/webidl.d.ts
@@ -8,7 +8,4 @@ declare type USVString = string;
 declare type DOMString = string;
 
 // see: https://fetch.spec.whatwg.org/#headersinit
-declare type OpenEndedDictionary = Object;
-
-declare class FormData { }
-declare class Blob { }
\ No newline at end of file
+declare type OpenEndedDictionary = Object;
\ No newline at end of file