diff --git a/lib/assert.js b/lib/assert.js
index df575c0..9315783 100644
--- a/lib/assert.js
+++ b/lib/assert.js
@@ -25,6 +25,7 @@ const compare = process.binding('buffer').compare;
 const util = require('util');
 const objectToString = require('internal/util').objectToString;
 const Buffer = require('buffer').Buffer;
+const errors = require('internal/errors');
 
 // The assert module provides functions that throw
 // AssertionError's when particular conditions are not met. The
@@ -391,7 +392,7 @@ function _throws(shouldThrow, block, expected, message) {
   var actual;
 
   if (typeof block !== 'function') {
-    throw new TypeError('"block" argument must be a function');
+    throw new errors.TypeError('ERR_ARG_FUNCTION');
   }
 
   if (typeof expected === 'string') {
diff --git a/lib/internal/errors.js b/lib/internal/errors.js
index 01e4e48..15198b4 100644
--- a/lib/internal/errors.js
+++ b/lib/internal/errors.js
@@ -80,4 +80,5 @@ module.exports = exports = {
 //
 // Note: Please try to keep these in alphabetical order
 E('ERR_ASSERTION', (msg) => msg);
+E('ERR_ARG_FUNCTION', '"block" argument must be a function');
 // Add new errors from here...

diff --git a/lib/internal/errors.js b/lib/internal/errors.js
index 01e4e482cb..363db9728b 100644
--- a/lib/internal/errors.js
+++ b/lib/internal/errors.js
@@ -6,7 +6,6 @@
 // value statically and permanently identifies the error. While the error
 // message may change, the code should not.

-const assert = require('assert');
 const kCode = Symbol('code');
 const messages = new Map();

@@ -36,10 +35,15 @@ function makeNodeError(Base) {
 }

 function message(key, args) {
-  assert.strictEqual(typeof key, 'string');
+  if (typeof key !== 'string')
+    throw new TypeError('"key" argument must be a string');
+
   const util = lazyUtil();
   const msg = messages.get(key);
-  assert(msg, `An invalid error message key was used: ${key}.`);
+
+  if (!msg)
+    throw new Error(`An invalid error message key was used: ${key}.`);
+
   let fmt = util.format;
   if (typeof msg === 'function') {
     fmt = msg;
@@ -54,7 +58,9 @@ function message(key, args) {
 // Utility function for registering the error codes. Only used here. Exported
 // *only* to allow for testing.
 function E(sym, val) {
-  assert(messages.has(sym) === false, `Error symbol: ${sym} was already used.`);
+  if (messages.has(sym))
+    throw new Error(`Error symbol: ${sym} was already used.`);
+
   messages.set(sym, typeof val === 'function' ? val : String(val));
 }