diff --git a/src/index.js b/src/index.js
index 08dd49e..f220efc 100644
--- a/src/index.js
+++ b/src/index.js
@@ -17,11 +17,16 @@ class PeerId {
       assert(privKey.public.bytes.equals(pubKey.bytes), 'inconsistent arguments')
     }
 
-    this.id = id
+    this._id = id
+    this._idB58String = ''
     this._privKey = privKey
     this._pubKey = pubKey
   }
 
+  get id () {
+    return this._id
+  }
+
   get privKey () {
     return this._privKey
   }
@@ -61,7 +66,7 @@ class PeerId {
   // of go-ipfs for its config file
   toJSON () {
     return {
-      id: mh.toB58String(this.id),
+      id: this.toB58String(),
       privKey: toB64Opt(this.marshalPrivKey()),
       pubKey: toB64Opt(this.marshalPubKey())
     }
@@ -77,7 +82,11 @@ class PeerId {
   }
 
   toB58String () {
-    return mh.toB58String(this.id)
+    if (!this._idB58String) {
+      this._idB58String = mh.toB58String(this.id)
+    }
+
+    return this._idB58String
   }
 }