diff --git a/src/mixed.js b/src/mixed.js
index f99cdfa7d..d6f67b952 100644
--- a/src/mixed.js
+++ b/src/mixed.js
@@ -1,4 +1,3 @@
-import typeOf from 'type-name';
 import has from 'lodash/has';
 
 import { mixed as locale } from './locale';
@@ -133,15 +132,23 @@ SchemaType.prototype = {
     return this
   },
 
-  cast(value, opts = {}) {
-    let schema = this.resolve(opts)
-
-    let result = schema._cast(value, opts);
-
-    if (opts.assert !== false && !this.isType(result)) {
+  cast(value, options = {}) {
+    let resolvedSchema = this.resolve(options)
+    let result = resolvedSchema._cast(value, options);
+
+    if (
+      value !== undefined &&
+      options.assert !== false &&
+      resolvedSchema.isType(result) !== true
+    ) {
+      let formattedValue = JSON.stringify(value);
+      let formattedResult = JSON.stringify(result);
       throw new TypeError(
-        `Expected ${opts.path || 'field'} to be type: "${this._type}". ` +
-        `Got "${typeOf(value)}" instead.`
+        `The value of ${options.path || 'field'} could not be cast to a value ` +
+        `that satisfies the schema type: "${resolvedSchema._type}". \n\n` +
+        `attempted value: ${JSON.stringify(value)} \n` +
+        ((formattedResult !== formattedValue)
+          ? `result of cast: ${JSON.stringify(result)}` : '')
       );
     }
 
diff --git a/test/helpers.js b/test/helpers.js
index d2c98d14e..ea2cb955a 100644
--- a/test/helpers.js
+++ b/test/helpers.js
@@ -1,10 +1,9 @@
-import typeOf from 'type-name';
 
 export let castAndShouldFail = (schema, value) => {
   (()=> schema.cast(value))
     .should.throw(
       TypeError,
-      new RegExp(`Got "${typeOf(value)}" instead`, 'gi')
+      /The value of (.+) could not be cast to a value that satisfies the schema type/gi
     )
 }
 
diff --git a/test/string.js b/test/string.js
index 91407ac07..6964a336c 100644
--- a/test/string.js
+++ b/test/string.js
@@ -19,7 +19,6 @@ describe('String types', function(){
         [null, null, schema.nullable()]
       ],
       invalid: [
-        undefined,
         null,
       ]
     })
diff --git a/test/yup.js b/test/yup.js
index f4e1d8381..a78be23cf 100644
--- a/test/yup.js
+++ b/test/yup.js
@@ -12,6 +12,24 @@ describe('Yup', function(){
     require('../lib')
   })
 
+  it('cast should not assert on undefined', () => {
+    (() => string().cast(undefined))
+      .should.not.throw()
+  })
+
+  it('cast should assert on undefined cast results', () => {
+    (() => string().transform(() => undefined).cast('foo'))
+      .should.throw()
+  })
+
+  it('cast should respect assert option', () => {
+    (() => string().cast(null))
+      .should.throw();
+
+    (() => string().cast(null, { assert: false }))
+      .should.not.throw()
+  })
+
   it('should do settled', function(){
     return Promise.all([