diff --git a/io/bufio.ts b/io/bufio.ts
index 99b5638161..dc6d6b3cc4 100644
--- a/io/bufio.ts
+++ b/io/bufio.ts
@@ -192,10 +192,10 @@ export class BufReader implements Reader {
     return p;
   }
 
-  /** Returns the next byte [0, 255] or -1 if EOF. */
-  async readByte(): Promise<number> {
+  /** Returns the next byte [0, 255] or `EOF`. */
+  async readByte(): Promise<number | EOF> {
     while (this.r === this.w) {
-      if (this.eof) return -1;
+      if (this.eof) return EOF;
       await this._fill(); // buffer is empty.
     }
     const c = this.buf[this.r];
diff --git a/io/bufio_test.ts b/io/bufio_test.ts
index 84b6f9142c..6433c7a5a8 100644
--- a/io/bufio_test.ts
+++ b/io/bufio_test.ts
@@ -35,7 +35,7 @@ async function readBytes(buf: BufReader): Promise<string> {
   let nb = 0;
   while (true) {
     let c = await buf.readByte();
-    if (c < 0) {
+    if (c === EOF) {
       break; // EOF
     }
     b[nb] = c;
diff --git a/io/ioutil.ts b/io/ioutil.ts
index 484aba2812..979549fbf2 100644
--- a/io/ioutil.ts
+++ b/io/ioutil.ts
@@ -1,5 +1,5 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import { BufReader } from "./bufio.ts";
+import { BufReader, EOF, UnexpectedEOFError } from "./bufio.ts";
 type Reader = Deno.Reader;
 type Writer = Deno.Writer;
 import { assert } from "../testing/asserts.ts";
@@ -30,36 +30,47 @@ export async function copyN(
 }
 
 /** Read big endian 16bit short from BufReader */
-export async function readShort(buf: BufReader): Promise<number> {
-  const [high, low] = [await buf.readByte(), await buf.readByte()];
+export async function readShort(buf: BufReader): Promise<number | EOF> {
+  const high = await buf.readByte();
+  if (high === EOF) return EOF;
+  const low = await buf.readByte();
+  if (low === EOF) throw new UnexpectedEOFError();
   return (high << 8) | low;
 }
 
 /** Read big endian 32bit integer from BufReader */
-export async function readInt(buf: BufReader): Promise<number> {
-  const [high, low] = [await readShort(buf), await readShort(buf)];
+export async function readInt(buf: BufReader): Promise<number | EOF> {
+  const high = await readShort(buf);
+  if (high === EOF) return EOF;
+  const low = await readShort(buf);
+  if (low === EOF) throw new UnexpectedEOFError();
   return (high << 16) | low;
 }
 
-const BIT32 = 0xffffffff;
+const MAX_SAFE_INTEGER = BigInt(Number.MAX_SAFE_INTEGER);
 
 /** Read big endian 64bit long from BufReader */
-export async function readLong(buf: BufReader): Promise<number> {
-  const [high, low] = [await readInt(buf), await readInt(buf)];
-  // ECMAScript doesn't support 64bit bit ops.
-  return high ? high * (BIT32 + 1) + low : low;
+export async function readLong(buf: BufReader): Promise<number | EOF> {
+  const high = await readInt(buf);
+  if (high === EOF) return EOF;
+  const low = await readInt(buf);
+  if (low === EOF) throw new UnexpectedEOFError();
+  const big = (BigInt(high) << 32n) | BigInt(low);
+  // We probably should provide a similar API that returns BigInt values.
+  if (big > MAX_SAFE_INTEGER) {
+    throw new RangeError(
+      "Long value too big to be represented as a Javascript number."
+    );
+  }
+  return Number(big);
 }
 
 /** Slice number into 64bit big endian byte array */
 export function sliceLongToBytes(d: number, dest = new Array(8)): number[] {
-  let mask = 0xff;
-  let low = (d << 32) >>> 32;
-  let high = (d - low) / (BIT32 + 1);
-  let shift = 24;
-  for (let i = 0; i < 4; i++) {
-    dest[i] = (high >>> shift) & mask;
-    dest[i + 4] = (low >>> shift) & mask;
-    shift -= 8;
+  let big = BigInt(d);
+  for (let i = 0; i < 8; i++) {
+    dest[7 - i] = Number(big & 0xffn);
+    big >>= 8n;
   }
   return dest;
 }
diff --git a/io/ioutil_test.ts b/io/ioutil_test.ts
index c1c1ded72a..4e34f56984 100644
--- a/io/ioutil_test.ts
+++ b/io/ioutil_test.ts
@@ -40,10 +40,10 @@ test(async function testReadInt(): Promise<void> {
 
 test(async function testReadLong(): Promise<void> {
   const r = new BinaryReader(
-    new Uint8Array([0x12, 0x34, 0x56, 0x78, 0x12, 0x34, 0x56, 0x78])
+    new Uint8Array([0x00, 0x00, 0x00, 0x78, 0x12, 0x34, 0x56, 0x78])
   );
   const long = await readLong(new BufReader(r));
-  assertEquals(long, 0x1234567812345678);
+  assertEquals(long, 0x7812345678);
 });
 
 test(async function testReadLong2(): Promise<void> {
diff --git a/ws/mod.ts b/ws/mod.ts
index 86ab2f045d..d74e4a92b6 100644
--- a/ws/mod.ts
+++ b/ws/mod.ts
@@ -142,6 +142,7 @@ export async function writeFrame(
 /** Read websocket frame from given BufReader */
 export async function readFrame(buf: BufReader): Promise<WebSocketFrame> {
   let b = await buf.readByte();
+  if (b === EOF) throw new UnexpectedEOFError();
   let isLastFrame = false;
   switch (b >>> 4) {
     case 0b1000:
@@ -156,12 +157,17 @@ export async function readFrame(buf: BufReader): Promise<WebSocketFrame> {
   const opcode = b & 0x0f;
   // has_mask & payload
   b = await buf.readByte();
+  if (b === EOF) throw new UnexpectedEOFError();
   const hasMask = b >>> 7;
   let payloadLength = b & 0b01111111;
   if (payloadLength === 126) {
-    payloadLength = await readShort(buf);
+    const l = await readShort(buf);
+    if (l === EOF) throw new UnexpectedEOFError();
+    payloadLength = l;
   } else if (payloadLength === 127) {
-    payloadLength = await readLong(buf);
+    const l = await readLong(buf);
+    if (l === EOF) throw new UnexpectedEOFError();
+    payloadLength = Number(l);
   }
   // mask
   let mask;