diff --git a/src/connection/connection.d.ts b/src/connection/connection.d.ts
index 41c289f..ff6f014 100644
--- a/src/connection/connection.d.ts
+++ b/src/connection/connection.d.ts
@@ -30,8 +30,8 @@ declare class Connection {
      * @param {string} [properties.stat.encryption] connection encryption method identifier.
      */
     constructor({ localAddr, remoteAddr, localPeer, remotePeer, newStream, close, getStreams, stat }: {
-        localAddr: multiaddr;
-        remoteAddr: multiaddr;
+        localAddr: multiaddr | undefined;
+        remoteAddr: multiaddr | undefined;
         localPeer: PeerId;
         remotePeer: PeerId;
         newStream: Function;
@@ -43,8 +43,8 @@ declare class Connection {
                 open: string;
                 upgraded: string;
             };
-            multiplexer: string;
-            encryption: string;
+            multiplexer: string | undefined;
+            encryption: string | undefined;
         };
     });
     /**
@@ -54,11 +54,11 @@ declare class Connection {
     /**
      * Observed multiaddr of the local peer
      */
-    localAddr: multiaddr;
+    localAddr: multiaddr | undefined;
     /**
      * Observed multiaddr of the remote peer
      */
-    remoteAddr: multiaddr;
+    remoteAddr: multiaddr | undefined;
     /**
      * Local peer id.
      */
@@ -77,8 +77,8 @@ declare class Connection {
             open: string;
             upgraded: string;
         };
-        multiplexer?: string;
-        encryption?: string;
+        multiplexer?: string | undefined;
+        encryption?: string | undefined;
     };
     /**
      * Reference to the new stream function of the multiplexer
@@ -113,8 +113,8 @@ declare class Connection {
             open: string;
             upgraded: string;
         };
-        multiplexer?: string;
-        encryption?: string;
+        multiplexer?: string | undefined;
+        encryption?: string | undefined;
     };
     /**
      * Get all the streams of the muxer.
diff --git a/src/pubsub/index.d.ts b/src/pubsub/index.d.ts
index a327bf7..cbb6881 100644
--- a/src/pubsub/index.d.ts
+++ b/src/pubsub/index.d.ts
@@ -34,9 +34,9 @@ declare class PubsubBaseProtocol {
         globalSignaturePolicy: {
             StrictSign: "StrictSign";
             StrictNoSign: string;
-        };
-        canRelayMessage: boolean;
-        emitSelf: boolean;
+        } | undefined;
+        canRelayMessage: boolean | undefined;
+        emitSelf: boolean | undefined;
     });
     log: any;
     /**
@@ -285,13 +285,13 @@ declare namespace PubsubBaseProtocol {
 }
 type PeerId = import("peer-id");
 type InMessage = {
-    from?: string;
+    from?: string | undefined;
     receivedFrom: string;
     topicIDs: string[];
-    seqno?: Uint8Array;
+    seqno?: Uint8Array | undefined;
     data: Uint8Array;
-    signature?: Uint8Array;
-    key?: Uint8Array;
+    signature?: Uint8Array | undefined;
+    key?: Uint8Array | undefined;
 };
 import PeerStreams = require("./peer-streams");
 /**
diff --git a/src/pubsub/utils.d.ts b/src/pubsub/utils.d.ts
index 1cc14a4..c400623 100644
--- a/src/pubsub/utils.d.ts
+++ b/src/pubsub/utils.d.ts
@@ -3,11 +3,11 @@ export function msgId(from: string, seqno: Uint8Array): Uint8Array;
 export function noSignMsgId(data: Uint8Array): Uint8Array;
 export function anyMatch(a: Set<any> | any[], b: Set<any> | any[]): boolean;
 export function ensureArray<T>(maybeArray: T | T[]): T[];
-export function normalizeInRpcMessage<T extends unknown>(message: T, peerId?: string): T & {
-    from?: string;
-    peerId?: string;
+export function normalizeInRpcMessage<T extends Object>(message: T, peerId?: string | undefined): T & {
+    from?: string | undefined;
+    peerId?: string | undefined;
 };
-export function normalizeOutRpcMessage<T extends unknown>(message: T): T & {
-    from?: Uint8Array;
-    data?: Uint8Array;
+export function normalizeOutRpcMessage<T extends Object>(message: T): T & {
+    from?: Uint8Array | undefined;
+    data?: Uint8Array | undefined;
 };
diff --git a/src/topology/index.d.ts b/src/topology/index.d.ts
index 70241f4..83bc5c9 100644
--- a/src/topology/index.d.ts
+++ b/src/topology/index.d.ts
@@ -17,12 +17,12 @@ declare class Topology {
      * @constructor
      */
     constructor({ min, max, handlers }: {
-        min: number;
-        max: number;
+        min: number | undefined;
+        max: number | undefined;
         handlers: {
-            onConnect: Function;
-            onDisconnect: Function;
-        };
+            onConnect?: Function | undefined;
+            onDisconnect?: Function | undefined;
+        } | undefined;
     });
     min: number;
     max: number;
diff --git a/src/topology/multicodec-topology.d.ts b/src/topology/multicodec-topology.d.ts
index 06d16f5..343e3f1 100644
--- a/src/topology/multicodec-topology.d.ts
+++ b/src/topology/multicodec-topology.d.ts
@@ -18,8 +18,8 @@ declare class MulticodecTopology extends Topology {
      * @constructor
      */
     constructor({ min, max, multicodecs, handlers }: {
-        min: number;
-        max: number;
+        min: number | undefined;
+        max: number | undefined;
         multicodecs: Array<string>;
         handlers: {
             onConnect: Function;
@@ -34,7 +34,7 @@ declare class MulticodecTopology extends Topology {
      * @param {Array<string>} props.protocols
      */
     _onProtocolChange({ peerId, protocols }: {
-        peerId: any;
+        peerId: PeerId;
         protocols: Array<string>;
     }): void;
     /**
@@ -42,18 +42,22 @@ declare class MulticodecTopology extends Topology {
      * @param {Connection} connection
      * @returns {void}
      */
-    _onPeerConnect(connection: any): void;
+    _onPeerConnect(connection: Connection): void;
     /**
      * Update topology.
      * @param {Array<{id: PeerId, multiaddrs: Array<Multiaddr>, protocols: Array<string>}>} peerDataIterable
      * @returns {void}
      */
     _updatePeers(peerDataIterable: Array<{
-        id: any;
-        multiaddrs: Array<any>;
+        id: PeerId;
+        multiaddrs: Array<Multiaddr>;
         protocols: Array<string>;
     }>): void;
-    get [multicodecTopologySymbol](): boolean;
+}
+declare namespace MulticodecTopology {
+    export { PeerId, Multiaddr, Connection };
 }
 import Topology = require(".");
-declare const multicodecTopologySymbol: unique symbol;
+type PeerId = import("peer-id");
+type Connection = typeof import("../connection");
+type Multiaddr = import("multiaddr");
diff --git a/tsconfig.json b/tsconfig.json
index 482bfe8..2902998 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -6,6 +6,7 @@
     // Tells TypeScript to read JS files, as
     // normally they are ignored as source files
     "allowJs": true,
+    "strict": true,
     // Generate d.ts files
     "declaration": true,
     // This compiler run should