diff --git a/index.d.ts b/index.d.ts
index 65faf63..f68ce8a 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -1,4 +1,8 @@
 /// <reference types="node" />
+
+// Note: marking anything protected or private in the exported
+// class will limit Minipass's ability to be used as the base
+// for mixin classes.
 import { EventEmitter } from 'events'
 import { Stream } from 'stream'
 
@@ -16,12 +20,6 @@ declare namespace Minipass {
     pipe(): any
   }
 
-  interface Pipe<R, W> {
-    src: Minipass<R, W>
-    dest: Writable
-    opts: PipeOptions
-  }
-
   type DualIterable<T> = Iterable<T> & AsyncIterable<T>
 
   type ContiguousData = Buffer | ArrayBufferLike | ArrayBufferView | string
@@ -76,12 +74,6 @@ declare class Minipass<
   readonly emittedEnd: boolean
   readonly destroyed: boolean
 
-  /**
-   * Not technically private or readonly, but not safe to mutate.
-   */
-  private readonly buffer: RType[]
-  private readonly pipes: Minipass.Pipe<RType, WType>[]
-
   /**
    * Technically writable, but mutating it can change the type,
    * so is not safe to do in TypeScript.
diff --git a/index.js b/index.js
index e8797aa..d5003ed 100644
--- a/index.js
+++ b/index.js
@@ -21,6 +21,8 @@ const DECODER = Symbol('decoder')
 const FLOWING = Symbol('flowing')
 const PAUSED = Symbol('paused')
 const RESUME = Symbol('resume')
+const BUFFER = Symbol('buffer')
+const PIPES = Symbol('pipes')
 const BUFFERLENGTH = Symbol('bufferLength')
 const BUFFERPUSH = Symbol('bufferPush')
 const BUFFERSHIFT = Symbol('bufferShift')
@@ -94,8 +96,8 @@ module.exports = class Minipass extends Stream {
     this[FLOWING] = false
     // whether we're explicitly paused
     this[PAUSED] = false
-    this.pipes = []
-    this.buffer = []
+    this[PIPES] = []
+    this[BUFFER] = []
     this[OBJECTMODE] = options && options.objectMode || false
     if (this[OBJECTMODE])
       this[ENCODING] = null
@@ -114,6 +116,12 @@ module.exports = class Minipass extends Stream {
     this.readable = true
     this[BUFFERLENGTH] = 0
     this[DESTROYED] = false
+    if (options && options.debugExposeBuffer === true) {
+      Object.defineProperty(this, 'buffer', { get: () => this[BUFFER] })
+    }
+    if (options && options.debugExposePipes === true) {
+      Object.defineProperty(this, 'pipes', { get: () => this[PIPES] })
+    }
   }
 
   get bufferLength () { return this[BUFFERLENGTH] }
@@ -129,8 +137,8 @@ module.exports = class Minipass extends Stream {
 
     if (this[ENCODING] !== enc) {
       this[DECODER] = enc ? new SD(enc) : null
-      if (this.buffer.length)
-        this.buffer = this.buffer.map(chunk => this[DECODER].write(chunk))
+      if (this[BUFFER].length)
+        this[BUFFER] = this[BUFFER].map(chunk => this[DECODER].write(chunk))
     }
 
     this[ENCODING] = enc
@@ -252,14 +260,14 @@ module.exports = class Minipass extends Stream {
     if (this[OBJECTMODE])
       n = null
 
-    if (this.buffer.length > 1 && !this[OBJECTMODE]) {
+    if (this[BUFFER].length > 1 && !this[OBJECTMODE]) {
       if (this.encoding)
-        this.buffer = [this.buffer.join('')]
+        this[BUFFER] = [this[BUFFER].join('')]
       else
-        this.buffer = [Buffer.concat(this.buffer, this[BUFFERLENGTH])]
+        this[BUFFER] = [Buffer.concat(this[BUFFER], this[BUFFERLENGTH])]
     }
 
-    const ret = this[READ](n || null, this.buffer[0])
+    const ret = this[READ](n || null, this[BUFFER][0])
     this[MAYBE_EMIT_END]()
     return ret
   }
@@ -268,14 +276,14 @@ module.exports = class Minipass extends Stream {
     if (n === chunk.length || n === null)
       this[BUFFERSHIFT]()
     else {
-      this.buffer[0] = chunk.slice(n)
+      this[BUFFER][0] = chunk.slice(n)
       chunk = chunk.slice(0, n)
       this[BUFFERLENGTH] -= n
     }
 
     this.emit('data', chunk)
 
-    if (!this.buffer.length && !this[EOF])
+    if (!this[BUFFER].length && !this[EOF])
       this.emit('drain')
 
     return chunk
@@ -310,7 +318,7 @@ module.exports = class Minipass extends Stream {
     this[PAUSED] = false
     this[FLOWING] = true
     this.emit('resume')
-    if (this.buffer.length)
+    if (this[BUFFER].length)
       this[FLUSH]()
     else if (this[EOF])
       this[MAYBE_EMIT_END]()
@@ -344,23 +352,23 @@ module.exports = class Minipass extends Stream {
       this[BUFFERLENGTH] += 1
     else
       this[BUFFERLENGTH] += chunk.length
-    this.buffer.push(chunk)
+    this[BUFFER].push(chunk)
   }
 
   [BUFFERSHIFT] () {
-    if (this.buffer.length) {
+    if (this[BUFFER].length) {
       if (this[OBJECTMODE])
         this[BUFFERLENGTH] -= 1
       else
-        this[BUFFERLENGTH] -= this.buffer[0].length
+        this[BUFFERLENGTH] -= this[BUFFER][0].length
     }
-    return this.buffer.shift()
+    return this[BUFFER].shift()
   }
 
   [FLUSH] (noDrain) {
     do {} while (this[FLUSHCHUNK](this[BUFFERSHIFT]()))
 
-    if (!noDrain && !this.buffer.length && !this[EOF])
+    if (!noDrain && !this[BUFFER].length && !this[EOF])
       this.emit('drain')
   }
 
@@ -385,7 +393,7 @@ module.exports = class Minipass extends Stream {
       if (opts.end)
         dest.end()
     } else {
-      this.pipes.push(!opts.proxyErrors ? new Pipe(this, dest, opts)
+      this[PIPES].push(!opts.proxyErrors ? new Pipe(this, dest, opts)
         : new PipeProxyErrors(this, dest, opts))
       if (this[ASYNC])
         defer(() => this[RESUME]())
@@ -397,9 +405,9 @@ module.exports = class Minipass extends Stream {
   }
 
   unpipe (dest) {
-    const p = this.pipes.find(p => p.dest === dest)
+    const p = this[PIPES].find(p => p.dest === dest)
     if (p) {
-      this.pipes.splice(this.pipes.indexOf(p), 1)
+      this[PIPES].splice(this[PIPES].indexOf(p), 1)
       p.unpipe()
     }
   }
@@ -410,7 +418,7 @@ module.exports = class Minipass extends Stream {
 
   on (ev, fn) {
     const ret = super.on(ev, fn)
-    if (ev === 'data' && !this.pipes.length && !this.flowing)
+    if (ev === 'data' && !this[PIPES].length && !this.flowing)
       this[RESUME]()
     else if (ev === 'readable' && this[BUFFERLENGTH] !== 0)
       super.emit('readable')
@@ -434,7 +442,7 @@ module.exports = class Minipass extends Stream {
     if (!this[EMITTING_END] &&
         !this[EMITTED_END] &&
         !this[DESTROYED] &&
-        this.buffer.length === 0 &&
+        this[BUFFER].length === 0 &&
         this[EOF]) {
       this[EMITTING_END] = true
       this.emit('end')
@@ -486,7 +494,7 @@ module.exports = class Minipass extends Stream {
   }
 
   [EMITDATA] (data) {
-    for (const p of this.pipes) {
+    for (const p of this[PIPES]) {
       if (p.dest.write(data) === false)
         this.pause()
     }
@@ -511,14 +519,14 @@ module.exports = class Minipass extends Stream {
     if (this[DECODER]) {
       const data = this[DECODER].end()
       if (data) {
-        for (const p of this.pipes) {
+        for (const p of this[PIPES]) {
           p.dest.write(data)
         }
         super.emit('data', data)
       }
     }
 
-    for (const p of this.pipes) {
+    for (const p of this[PIPES]) {
       p.end()
     }
     const ret = super.emit('end')
@@ -625,7 +633,7 @@ module.exports = class Minipass extends Stream {
     this[DESTROYED] = true
 
     // throw away all buffered data, it's never coming out
-    this.buffer.length = 0
+    this[BUFFER].length = 0
     this[BUFFERLENGTH] = 0
 
     if (typeof this.close === 'function' && !this[CLOSED])
diff --git a/test/basic.js b/test/basic.js
index e8c9627..67620b1 100644
--- a/test/basic.js
+++ b/test/basic.js
@@ -3,7 +3,7 @@ const t = require('tap')
 const EE = require('events').EventEmitter
 
 t.test('some basic piping and writing', async t => {
-  let mp = new MiniPass({ encoding: 'base64' })
+  let mp = new MiniPass({ encoding: 'base64', debugExposeBuffer: true })
   t.notOk(mp.flowing)
   mp.flowing = true
   t.notOk(mp.flowing)
@@ -13,7 +13,7 @@ t.test('some basic piping and writing', async t => {
   t.equal(mp.readable, true)
   t.equal(mp.writable, true)
   t.equal(mp.write('hello'), false)
-  let dest = new MiniPass()
+  let dest = new MiniPass({ debugExposeBuffer: true })
   let sawDestData = false
   dest.once('data', chunk => {
     sawDestData = true
@@ -279,7 +279,7 @@ t.test('emit works with many args', t => {
 })
 
 t.test('emit drain on resume, even if no flush', t => {
-  const mp = new MiniPass()
+  const mp = new MiniPass({ debugExposeBuffer: true })
   mp.encoding = 'utf8'
 
   const chunks = []
diff --git a/test/unpipe.js b/test/unpipe.js
index 5a97c0a..f24ec3d 100644
--- a/test/unpipe.js
+++ b/test/unpipe.js
@@ -1,7 +1,7 @@
 const t = require('tap')
 const Minipass = require('../')
 
-const src = new Minipass({ encoding: 'utf8' })
+const src = new Minipass({ encoding: 'utf8', debugExposePipes: true })
 const dest = new Minipass({ encoding: 'utf8' })
 const dest2 = new Minipass({ encoding: 'utf8' })
 const destOut = []