diff --git a/ext/descriptor/README.md b/ext/descriptor/README.md
index 95df5a885..dff1bef32 100644
--- a/ext/descriptor/README.md
+++ b/ext/descriptor/README.md
@@ -10,7 +10,7 @@ Usage
 var protobuf   = require("protobufjs"),
     descriptor = require("protobufjs/ext/descriptor");
 
-var descriptor = ...; // either a FieldDescriptorSet buffer or JSON object
+var descriptor = ...; // either a FieldDescriptorSet buffer, a FieldDescriptorSet message instance or a corresponding valid JSON object
 var root = protobuf.Root.fromDescriptor(descriptor);
 var rootDescriptor = root.toDescriptor("proto3");
 ```
@@ -18,4 +18,4 @@ var rootDescriptor = root.toDescriptor("proto3");
 API
 ---
 
-The extension adds `.fromDescriptor(descriptor[, syntax])` and `#toDescriptor([syntax])` methods to reflection objects and exports the internally used `Root` instance that contains the types present in descriptor.proto.
+The extension adds `.fromDescriptor(descriptor[, syntax])` and `#toDescriptor([syntax])` methods to reflection objects and exports the `.google.protobuf` namespace of the internally used `Root` instance containing the types present in descriptor.proto.
diff --git a/ext/descriptor/index.d.ts b/ext/descriptor/index.d.ts
index 849ea236d..7f3c43f55 100644
--- a/ext/descriptor/index.d.ts
+++ b/ext/descriptor/index.d.ts
@@ -1,6 +1,6 @@
 import * as $protobuf from "../..";
 
-declare const descriptor: $protobuf.Root;
+declare const descriptor: $protobuf.Namespace;
 
 interface IFileDescriptorSet {
     file: IFileDescriptorProto[];
diff --git a/ext/descriptor/index.js b/ext/descriptor/index.js
index 9959b40e0..f07243c50 100644
--- a/ext/descriptor/index.js
+++ b/ext/descriptor/index.js
@@ -4,13 +4,15 @@ var $protobuf = require("..");
 
 /**
  * Descriptor extension (ext/descriptor).
+ * Exports the `.google.protobuf` namespace of the internally used {@link Root} instance containing the types present in descriptor.proto.
  * @type {Root}
- * @tstype $protobuf.Root
+ * @tstype $protobuf.Namespace
  * @const
+ * @see https://github.com/dcodeIO/protobuf.js/tree/master/ext/descriptor
  */
 var descriptor = module.exports = $protobuf.Root.fromJSON(require("../google/protobuf/descriptor.json")).lookup(".google.protobuf");
 
-var google   = descriptor,
+var google   = descriptor, // aliased used where `descriptor` is a local var
     Root     = $protobuf.Root,
     Enum     = $protobuf.Enum,
     Type     = $protobuf.Type,
@@ -44,7 +46,7 @@ var google   = descriptor,
 
 /**
  * Creates a root from a descriptor set.
- * @param {Properties<IFileDescriptorSet>|Reader|Uint8Array} descriptor Descriptor
+ * @param {IFileDescriptorSet|Reader|Uint8Array} descriptor Descriptor
  * @returns {Root} Root instance
  * @see Part of the {@link descriptor} extension (ext/descriptor)
  */
@@ -144,7 +146,7 @@ var unnamedMessageIndex = 0;
 
 /**
  * Creates a type from a descriptor.
- * @param {Properties<IDescriptorProto>|Reader|Uint8Array} descriptor Descriptor
+ * @param {IDescriptorProto|Reader|Uint8Array} descriptor Descriptor
  * @param {string} [syntax="proto2"] Syntax
  * @returns {Type} Type instance
  * @see Part of the {@link descriptor} extension (ext/descriptor)
@@ -520,7 +522,7 @@ var unnamedServiceIndex = 0;
 
 /**
  * Creates a service from a descriptor.
- * @param {Properties<IServiceDescriptorProto>|Reader|Uint8Array} descriptor Descriptor
+ * @param {IServiceDescriptorProto|Reader|Uint8Array} descriptor Descriptor
  * @returns {Service} Service instance
  * @see Part of the {@link descriptor} extension (ext/descriptor)
  */