diff --git a/packages/abi/src.ts/interface.ts b/packages/abi/src.ts/interface.ts
index 54b54bcc4..73de0f0c1 100644
--- a/packages/abi/src.ts/interface.ts
+++ b/packages/abi/src.ts/interface.ts
@@ -55,7 +55,7 @@ export class Interface {
 
     readonly _abiCoder: AbiCoder;
 
-    static _isInterface: boolean;
+    readonly _isInterface: boolean;
 
     constructor(fragments: string | Array<Fragment | JsonFragment | string>) {
         logger.checkNew(new.target, Interface);
@@ -87,7 +87,7 @@ export class Interface {
                         logger.warn("duplicate definition - constructor");
                         return;
                     }
-                    defineReadOnly(this, "deploy", fragment);
+                    defineReadOnly(this, "deploy", <ConstructorFragment>fragment);
                     return;
                 case "function":
                     bucket = this.functions;
diff --git a/packages/asm/src.ts/assembler.ts b/packages/asm/src.ts/assembler.ts
index fe2cf7212..c415a6936 100644
--- a/packages/asm/src.ts/assembler.ts
+++ b/packages/asm/src.ts/assembler.ts
@@ -155,7 +155,7 @@ export abstract class Node {
         ethers.utils.defineReadOnly(this, "warnings", [ ]);
 
         for (const key in options) {
-            ethers.utils.defineReadOnly(this, key, options[key]);
+            ethers.utils.defineReadOnly<any, any>(this, key, options[key]);
         }
     }
 
@@ -702,11 +702,11 @@ class Assembler {
 
     readonly defines: { [ name: string ]: any };
 
-    private _stack: Array<Node>;
-    private _parents: { [ tag: string ]: Node };
-    private _script: Script;
+    _stack: Array<Node>;
+    _parents: { [ tag: string ]: Node };
+    _script: Script;
 
-    private _changed: boolean;
+    _changed: boolean;
 
     constructor(root: Node, options: AssemblerOptions) {
         ethers.utils.defineReadOnly(this, "positionIndependentCode", !!options.positionIndependentCode);
@@ -718,7 +718,7 @@ class Assembler {
 
 
         const nodes: { [ tag: string ]: NodeState } = { };
-        const labels: { [ name: string ]: Node } = { };
+        const labels: { [ name: string ]: LabelledNode } = { };
         const parents: { [ tag: string ]: Node } = { };
 
         // Link labels to their target node
diff --git a/packages/basex/src.ts/index.ts b/packages/basex/src.ts/index.ts
index a99e9905b..6f93a33d6 100644
--- a/packages/basex/src.ts/index.ts
+++ b/packages/basex/src.ts/index.ts
@@ -45,8 +45,8 @@ export class BaseX {
     readonly alphabet: string;
     readonly base: number;
 
-    private _alphabetMap: { [ character: string ]: number };
-    private _leader: string;
+    _alphabetMap: { [ character: string ]: number };
+    _leader: string;
 
     constructor(alphabet: string) {
         defineReadOnly(this, "alphabet", alphabet);
diff --git a/packages/cli/src.ts/bin/ethers-ens.ts b/packages/cli/src.ts/bin/ethers-ens.ts
index 59e4de410..739804005 100644
--- a/packages/cli/src.ts/bin/ethers-ens.ts
+++ b/packages/cli/src.ts/bin/ethers-ens.ts
@@ -241,18 +241,12 @@ abstract class AccountPlugin extends EnsPlugin {
     }
 
     async _setValue(key: string, value: string): Promise<void> {
-        ethers.utils.defineReadOnly(this, key, value);
+        ethers.utils.defineReadOnly<any, any>(this, key, value);
         if (key === "name") {
             await this._setValue("nodehash", ethers.utils.namehash(value));
         }
     }
 
-    async prepareOptions(argParser: ArgParser): Promise<void> {
-        await super.prepareOptions(argParser);
-
-        ethers.utils.defineReadOnly(this, "_wait", argParser.consumeFlag("wait"));
-    }
-
     async prepareArgs(args: Array<string>): Promise<void> {
         await super.prepareArgs(args);
 
diff --git a/packages/cli/src.ts/cli.ts b/packages/cli/src.ts/cli.ts
index 605a89a83..2b4c89118 100644
--- a/packages/cli/src.ts/cli.ts
+++ b/packages/cli/src.ts/cli.ts
@@ -491,7 +491,7 @@ export abstract class Plugin {
     network: ethers.providers.Network;
     provider: ethers.providers.Provider;
 
-    accounts: Array<WrappedSigner>;
+    accounts: ReadonlyArray<WrappedSigner>;
     mnemonicPassword: boolean;
     _xxxMnemonicPasswordHard: boolean;
 
diff --git a/packages/contracts/src.ts/index.ts b/packages/contracts/src.ts/index.ts
index b365ab9d0..5c00ba2b1 100644
--- a/packages/contracts/src.ts/index.ts
+++ b/packages/contracts/src.ts/index.ts
@@ -477,7 +477,7 @@ export class Contract {
             const uniqueFilters: { [ name: string ]: Array<string> } = { };
             Object.keys(this.interface.events).forEach((eventSignature) => {
                 const event = this.interface.events[eventSignature];
-                defineReadOnly(this.filters, eventSignature, (...args: Array<any>) => {
+                defineReadOnly<any, any>(this.filters, eventSignature, (...args: Array<any>) => {
                     return {
                         address: this.address,
                         topics: this.interface.encodeFilterTopics(event, args)
@@ -526,7 +526,7 @@ export class Contract {
             const run = runMethod(this, name, { });
 
             if (this[name] == null) {
-                defineReadOnly(this, name, run);
+                defineReadOnly<any, any>(this, name, run);
             }
 
             if (this.functions[name] == null) {
diff --git a/packages/properties/src.ts/index.ts b/packages/properties/src.ts/index.ts
index 1ad3991c3..408f01997 100644
--- a/packages/properties/src.ts/index.ts
+++ b/packages/properties/src.ts/index.ts
@@ -4,7 +4,7 @@ import { Logger } from "@ethersproject/logger";
 import { version } from "./_version";
 const logger = new Logger(version);
 
-export function defineReadOnly(object: any, name: string, value: any): void {
+export function defineReadOnly<T, K extends keyof T>(object: T, name: K, value: T[K]): void {
     Object.defineProperty(object, name, {
         enumerable: true,
         value: value,
diff --git a/packages/providers/src.ts/fallback-provider.ts b/packages/providers/src.ts/fallback-provider.ts
index d2227eda1..1da90f0c1 100644
--- a/packages/providers/src.ts/fallback-provider.ts
+++ b/packages/providers/src.ts/fallback-provider.ts
@@ -298,7 +298,7 @@ function getRunner(provider: Provider, method: string, params: { [ key: string]:
 }
 
 export class FallbackProvider extends BaseProvider {
-    readonly providerConfigs: Array<FallbackProviderConfig>;
+    readonly providerConfigs: ReadonlyArray<FallbackProviderConfig>;
     readonly quorum: number;
 
     // Due to teh highly asyncronous nature of the blockchain, we need
diff --git a/packages/providers/src.ts/url-json-rpc-provider.ts b/packages/providers/src.ts/url-json-rpc-provider.ts
index 6c20f0c4f..b57259d1c 100644
--- a/packages/providers/src.ts/url-json-rpc-provider.ts
+++ b/packages/providers/src.ts/url-json-rpc-provider.ts
@@ -1,3 +1,4 @@
+
 "use strict";
 
 import { Network, Networkish } from "@ethersproject/networks";
@@ -30,7 +31,7 @@ export abstract class UrlJsonRpcProvider extends JsonRpcProvider {
             defineReadOnly(this, "apiKey", apiKey);
         } else if (apiKey != null) {
             Object.keys(apiKey).forEach((key) => {
-                defineReadOnly(this, key, apiKey[key]);
+                defineReadOnly<any, any>(this, key, apiKey[key]);
             });
         }
     }
diff --git a/packages/wallet/src.ts/index.ts b/packages/wallet/src.ts/index.ts
index 7a04937b0..c8187ddfd 100644
--- a/packages/wallet/src.ts/index.ts
+++ b/packages/wallet/src.ts/index.ts
@@ -67,7 +67,6 @@ export class Wallet extends Signer implements ExternallyOwnedAccount {
                 }
             } else {
                 defineReadOnly(this, "_mnemonic", (): Mnemonic => null);
-                defineReadOnly(this, "path", null);
             }
 
 
@@ -82,7 +81,6 @@ export class Wallet extends Signer implements ExternallyOwnedAccount {
                 defineReadOnly(this, "_signingKey", () => signingKey);
             }
             defineReadOnly(this, "_mnemonic", (): Mnemonic => null);
-            defineReadOnly(this, "path", null);
             defineReadOnly(this, "address", computeAddress(this.publicKey));
         }