diff --git a/flow-typed/npm/jest_v22.x.x.js b/flow-typed/npm/jest_v22.x.x.js
index b107890..2ade5dc 100644
--- a/flow-typed/npm/jest_v22.x.x.js
+++ b/flow-typed/npm/jest_v22.x.x.js
@@ -436,24 +436,29 @@ type JestSpyType = {
   calls: JestCallsType
 };
 
+type JestDoneFn = {
+  (): void,
+  fail: (error: Error) => void,
+};
+
 /** Runs this function after every test inside this context */
 declare function afterEach(
-  fn: (done: () => void) => ?Promise<mixed>,
+  fn: (done: JestDoneFn) => ?Promise<mixed>,
   timeout?: number
 ): void;
 /** Runs this function before every test inside this context */
 declare function beforeEach(
-  fn: (done: () => void) => ?Promise<mixed>,
+  fn: (done: JestDoneFn) => ?Promise<mixed>,
   timeout?: number
 ): void;
 /** Runs this function after all tests have finished inside this context */
 declare function afterAll(
-  fn: (done: () => void) => ?Promise<mixed>,
+  fn: (done: JestDoneFn) => ?Promise<mixed>,
   timeout?: number
 ): void;
 /** Runs this function before any tests have started inside this context */
 declare function beforeAll(
-  fn: (done: () => void) => ?Promise<mixed>,
+  fn: (done: JestDoneFn) => ?Promise<mixed>,
   timeout?: number
 ): void;
 
@@ -486,7 +491,7 @@ declare var it: {
    */
   (
     name: string,
-    fn?: (done: () => void) => ?Promise<mixed>,
+    fn?: (done: JestDoneFn) => ?Promise<mixed>,
     timeout?: number
   ): void,
   /**
@@ -498,7 +503,7 @@ declare var it: {
    */
   only(
     name: string,
-    fn?: (done: () => void) => ?Promise<mixed>,
+    fn?: (done: JestDoneFn) => ?Promise<mixed>,
     timeout?: number
   ): void,
   /**
@@ -510,7 +515,7 @@ declare var it: {
    */
   skip(
     name: string,
-    fn?: (done: () => void) => ?Promise<mixed>,
+    fn?: (done: JestDoneFn) => ?Promise<mixed>,
     timeout?: number
   ): void,
   /**
@@ -522,13 +527,13 @@ declare var it: {
    */
   concurrent(
     name: string,
-    fn?: (done: () => void) => ?Promise<mixed>,
+    fn?: (done: JestDoneFn) => ?Promise<mixed>,
     timeout?: number
   ): void
 };
 declare function fit(
   name: string,
-  fn: (done: () => void) => ?Promise<mixed>,
+  fn: (done: JestDoneFn) => ?Promise<mixed>,
   timeout?: number
 ): void;
 /** An individual test unit */
diff --git a/package.json b/package.json
index 88f0e84..2aa6dcb 100644
--- a/package.json
+++ b/package.json
@@ -40,7 +40,7 @@
     "README.md"
   ],
   "peerDependencies": {
-    "graphql": "^0.5.0 || ^0.6.0 || ^0.7.0 || ^0.8.0-b || ^0.9.0 || ^0.10.0 || ^0.11.0 || ^0.12.0 || ^0.13.0 || ^14.0.0"
+    "graphql": "^0.5.0 || ^0.6.0 || ^0.7.0 || ^0.8.0-b || ^0.9.0 || ^0.10.0 || ^0.11.0 || ^0.12.0 || ^0.13.0 || ^14.0.0 || ^14.2.0"
   },
   "devDependencies": {
     "babel-cli": "^6.26.0",
@@ -51,8 +51,8 @@
     "babel-preset-stage-2": "^6.24.1",
     "codecov": "^3.0.0",
     "eslint-plugin-flowtype": "^2.50.0",
-    "flow-bin": "^0.81.0",
-    "graphql": "^14.0.2",
+    "flow-bin": "^0.107.0",
+    "graphql": "^14.2.1",
     "jest": "^23.6.0",
     "mockdate": "^2.0.2",
     "standard": "^12.0.1"
diff --git a/src/date/__snapshots__/index.test.js.snap b/src/date/__snapshots__/index.test.js.snap
index d032655..dd6c89b 100644
--- a/src/date/__snapshots__/index.test.js.snap
+++ b/src/date/__snapshots__/index.test.js.snap
@@ -39,3 +39,5 @@ exports[`GraphQLDate value parsing throws an error when parsing 4566 1`] = `"Dat
 exports[`GraphQLDate value parsing throws an error when parsing null 1`] = `"Date cannot represent non string type null"`;
 
 exports[`GraphQLDate value parsing throws an error when parsing true 1`] = `"Date cannot represent non string type true"`;
+
+exports[`GraphQLDate value parsing throws an error when parsing undefined 1`] = `"Date cannot represent non string type undefined"`;
diff --git a/src/date/index.js b/src/date/index.js
index 02c83d3..85a02a1 100644
--- a/src/date/index.js
+++ b/src/date/index.js
@@ -37,22 +37,24 @@ const config: GraphQLScalarTypeConfig<Date, string> = {
       throw new TypeError('Date cannot represent an invalid Date instance')
     } else if (typeof value === 'string' || value instanceof String) {
       if (validateDate(value)) {
-        return value
+        return value.toString()
       }
       throw new TypeError(
-        `Date cannot represent an invalid date-string ${value}.`
+        `Date cannot represent an invalid date-string ${value.toString()}.`
       )
     } else {
+      let parsedValue: string = JSON.stringify(value) || 'undefined'
       throw new TypeError(
         'Date cannot represent a non string, or non Date type ' +
-          JSON.stringify(value)
+          parsedValue
       )
     }
   },
   parseValue (value) {
     if (!(typeof value === 'string' || value instanceof String)) {
+      let parsedValue: string = JSON.stringify(value) || 'undefined'
       throw new TypeError(
-        `Date cannot represent non string type ${JSON.stringify(value)}`
+        `Date cannot represent non string type ${parsedValue}`
       )
     }
 
@@ -60,7 +62,7 @@ const config: GraphQLScalarTypeConfig<Date, string> = {
       return parseDate(value)
     }
     throw new TypeError(
-      `Date cannot represent an invalid date-string ${value}.`
+      `Date cannot represent an invalid date-string ${value.toString()}.`
     )
   },
   parseLiteral (ast) {
diff --git a/src/date/index.test.js b/src/date/index.test.js
index 0051bac..2b32f3a 100644
--- a/src/date/index.test.js
+++ b/src/date/index.test.js
@@ -93,7 +93,8 @@ describe('GraphQLDate', () => {
       {},
       [],
       true,
-      null
+      null,
+      undefined
     ].forEach(invalidInput => {
       it(`throws an error when parsing ${stringify(invalidInput)}`, () => {
         expect(() =>
diff --git a/src/dateTime/__snapshots__/index.test.js.snap b/src/dateTime/__snapshots__/index.test.js.snap
index cdcd2eb..3b75d52 100644
--- a/src/dateTime/__snapshots__/index.test.js.snap
+++ b/src/dateTime/__snapshots__/index.test.js.snap
@@ -73,3 +73,5 @@ exports[`GraphQLDateTime value parsing throws an error when parsing 4566 1`] = `
 exports[`GraphQLDateTime value parsing throws an error when parsing null 1`] = `"DateTime cannot represent non string type null"`;
 
 exports[`GraphQLDateTime value parsing throws an error when parsing true 1`] = `"DateTime cannot represent non string type true"`;
+
+exports[`GraphQLDateTime value parsing throws an error when parsing undefined 1`] = `"DateTime cannot represent non string type undefined"`;
diff --git a/src/dateTime/index.js b/src/dateTime/index.js
index 38872b3..41b5def 100644
--- a/src/dateTime/index.js
+++ b/src/dateTime/index.js
@@ -49,26 +49,28 @@ const config: GraphQLScalarTypeConfig<Date, string> = {
         return serializeDateTimeString(value)
       }
       throw new TypeError(
-        `DateTime cannot represent an invalid date-time-string ${value}.`
+        `DateTime cannot represent an invalid date-time-string ${value.toString()}.`
       )
     } else if (typeof value === 'number' || value instanceof Number) {
       if (validateUnixTimestamp(value)) {
         return serializeUnixTimestamp(value)
       }
       throw new TypeError(
-        'DateTime cannot represent an invalid Unix timestamp ' + value
+        'DateTime cannot represent an invalid Unix timestamp ' + value.valueOf()
       )
     } else {
+      let parsedValue: string = JSON.stringify(value) || 'undefined'
       throw new TypeError(
         'DateTime cannot be serialized from a non string, ' +
-        'non numeric or non Date type ' + JSON.stringify(value)
+        'non numeric or non Date type ' + parsedValue
       )
     }
   },
   parseValue (value) {
     if (!(typeof value === 'string' || value instanceof String)) {
+      let parsedValue: string = JSON.stringify(value) || 'undefined'
       throw new TypeError(
-        `DateTime cannot represent non string type ${JSON.stringify(value)}`
+        `DateTime cannot represent non string type ${parsedValue}`
       )
     }
 
@@ -76,7 +78,7 @@ const config: GraphQLScalarTypeConfig<Date, string> = {
       return parseDateTime(value)
     }
     throw new TypeError(
-      `DateTime cannot represent an invalid date-time-string ${value}.`
+      `DateTime cannot represent an invalid date-time-string ${value.toString()}.`
     )
   },
   parseLiteral (ast) {
diff --git a/src/dateTime/index.test.js b/src/dateTime/index.test.js
index 148eadb..6006a99 100644
--- a/src/dateTime/index.test.js
+++ b/src/dateTime/index.test.js
@@ -146,7 +146,8 @@ describe('GraphQLDateTime', () => {
       {},
       [],
       true,
-      null
+      null,
+      undefined
     ].forEach(invalidInput => {
       it(`throws an error when parsing ${stringify(invalidInput)}`, () => {
         expect(() =>
diff --git a/src/time/__snapshots__/index.test.js.snap b/src/time/__snapshots__/index.test.js.snap
index 83f205c..aefc226 100644
--- a/src/time/__snapshots__/index.test.js.snap
+++ b/src/time/__snapshots__/index.test.js.snap
@@ -53,3 +53,5 @@ exports[`GraphQLTime value parsing throws an error when parsing 4566 1`] = `"Tim
 exports[`GraphQLTime value parsing throws an error when parsing null 1`] = `"Time cannot represent non string type null"`;
 
 exports[`GraphQLTime value parsing throws an error when parsing true 1`] = `"Time cannot represent non string type true"`;
+
+exports[`GraphQLTime value parsing throws an error when parsing undefined 1`] = `"Time cannot represent non string type undefined"`;
diff --git a/src/time/index.js b/src/time/index.js
index bad791d..94df33e 100644
--- a/src/time/index.js
+++ b/src/time/index.js
@@ -47,19 +47,21 @@ const config: GraphQLScalarTypeConfig<Date, string> = {
         return serializeTimeString(value)
       }
       throw new TypeError(
-        `Time cannot represent an invalid time-string ${value}.`
+        `Time cannot represent an invalid time-string ${value.toString()}.`
       )
     } else {
+      let parsedValue: string = JSON.stringify(value) || 'undefined'
       throw new TypeError(
         'Time cannot be serialized from a non string, ' +
-        'or non Date type ' + JSON.stringify(value)
+        'or non Date type ' + parsedValue
       )
     }
   },
   parseValue (value: mixed): Date {
     if (!(typeof value === 'string' || value instanceof String)) {
+      let parsedValue: string = JSON.stringify(value) || 'undefined'
       throw new TypeError(
-        `Time cannot represent non string type ${JSON.stringify(value)}`
+        `Time cannot represent non string type ${parsedValue}`
       )
     }
 
@@ -67,7 +69,7 @@ const config: GraphQLScalarTypeConfig<Date, string> = {
       return parseTime(value)
     }
     throw new TypeError(
-      `Time cannot represent an invalid time-string ${value}.`
+      `Time cannot represent an invalid time-string ${value.toString()}.`
     )
   },
   parseLiteral (ast): ?Date {
diff --git a/src/time/index.test.js b/src/time/index.test.js
index f219fa8..a7ad5d8 100644
--- a/src/time/index.test.js
+++ b/src/time/index.test.js
@@ -112,7 +112,8 @@ describe('GraphQLTime', () => {
       {},
       [],
       true,
-      null
+      null,
+      undefined
     ].forEach(invalidInput => {
       it(`throws an error when parsing ${stringify(invalidInput)}`, () => {
         expect(() =>
diff --git a/src/utils/formatter.js b/src/utils/formatter.js
index a9cce5c..f785a27 100644
--- a/src/utils/formatter.js
+++ b/src/utils/formatter.js
@@ -16,9 +16,9 @@
 // Suppose the current date is 2016-01-01, then
 // parseTime('11:00:12Z') parses to a Date corresponding to
 // 2016-01-01T11:00:12Z.
-export const parseTime = (time: string): Date => {
+export const parseTime = (time: string | String): Date => {
   const currentDateString = new Date().toISOString()
-  return new Date(currentDateString.substr(0, currentDateString.indexOf('T') + 1) + time)
+  return new Date(currentDateString.substr(0, currentDateString.indexOf('T') + 1) + time.toString())
 }
 
 // Serializes a Date into an RFC 3339 compliant time-string in the
@@ -30,10 +30,10 @@ export const serializeTime = (date: Date): string => {
 
 // Serializes an RFC 3339 compliant time-string by shifting
 // it to UTC.
-export const serializeTimeString = (time: string): string => {
+export const serializeTimeString = (time: string | String): string => {
   // If already formatted to UTC then return the time string
   if (time.indexOf('Z') !== -1) {
-    return time
+    return time.toString()
   } else {
     // These are time-strings with timezone information,
     // these need to be shifted to UTC.
@@ -72,8 +72,8 @@ export const serializeTimeString = (time: string): string => {
 // Example:
 // parseDate('2016-01-01') parses to a Date corresponding to
 // 2016-01-01T00:00:00.000Z.
-export const parseDate = (date: string): Date => {
-  return new Date(date)
+export const parseDate = (date: string | String): Date => {
+  return new Date(date.toString())
 }
 
 // Serializes a Date into a RFC 3339 compliant date-string
@@ -83,8 +83,8 @@ export const serializeDate = (date: Date): string => {
 }
 
 // Parses an RFC 3339 compliant date-time-string into a Date.
-export const parseDateTime = (dateTime: string): Date => {
-  return new Date(dateTime)
+export const parseDateTime = (dateTime: string | String): Date => {
+  return new Date(dateTime.toString())
 }
 
 // Serializes a Date into an RFC 3339 compliant date-time-string
@@ -95,7 +95,8 @@ export const serializeDateTime = (dateTime: Date): string => {
 
 // Serializes an RFC 3339 compliant date-time-string by shifting
 // it to UTC.
-export const serializeDateTimeString = (dateTime: string): string => {
+export const serializeDateTimeString = (dateTime: string | String): string => {
+  dateTime = dateTime.toString()
   // If already formatted to UTC then return the time string
   if (dateTime.indexOf('Z') !== -1) {
     return dateTime
@@ -132,6 +133,6 @@ export const serializeDateTimeString = (dateTime: string): string => {
 
 // Serializes a Unix timestamp to an RFC 3339 compliant date-time-string
 // in the format YYYY-MM-DDThh:mm:ss.sssZ
-export const serializeUnixTimestamp = (timestamp: number): string => {
-  return new Date(timestamp * 1000).toISOString()
+export const serializeUnixTimestamp = (timestamp: number | Number): string => {
+  return new Date(timestamp.valueOf() * 1000).toISOString()
 }
diff --git a/src/utils/validator.js b/src/utils/validator.js
index 7562fb6..214c9db 100644
--- a/src/utils/validator.js
+++ b/src/utils/validator.js
@@ -44,8 +44,9 @@ const leapYear = (year: number): boolean => {
 //   equals NaN.
 // - Leap seconds cannot be known in advance.
 //
-export const validateTime = (time: string): boolean => {
+export const validateTime = (time: string | String): boolean => {
   const TIME_REGEX = /^([01][0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9])(\.\d{1,})?(([Z])|([+|-]([01][0-9]|2[0-3]):[0-5][0-9]))$/
+  time = time.toString()
   return TIME_REGEX.test(time)
 }
 
@@ -72,8 +73,9 @@ export const validateTime = (time: string): boolean => {
 // 11            November             30
 // 12            December             31
 //
-export const validateDate = (datestring: string): boolean => {
+export const validateDate = (datestring: string | String): boolean => {
   const RFC_3339_REGEX = /^(\d{4}-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01]))$/
+  datestring = datestring.toString()
 
   if (!RFC_3339_REGEX.test(datestring)) {
     return false
@@ -117,8 +119,9 @@ export const validateDate = (datestring: string): boolean => {
 //
 // Where *s is a fraction of seconds with at least 1 digit.
 //
-export const validateDateTime = (dateTimeString: string): boolean => {
+export const validateDateTime = (dateTimeString: string | String): boolean => {
   const RFC_3339_REGEX = /^(\d{4}-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])T([01][0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9]|60))(\.\d{1,})?(([Z])|([+|-]([01][0-9]|2[0-3]):[0-5][0-9]))$/
+  dateTimeString = dateTimeString.toString()
 
   // Validate the structure of the date-string
   if (!RFC_3339_REGEX.test(dateTimeString)) {
@@ -144,7 +147,8 @@ export const validateDateTime = (dateTimeString: string): boolean => {
 // Unix timestamps are signed 32-bit integers. They are interpreted
 // as the number of seconds since 00:00:00 UTC on 1 January 1970.
 //
-export const validateUnixTimestamp = (timestamp: number): boolean => {
+export const validateUnixTimestamp = (timestamp: number | Number): boolean => {
+  timestamp = timestamp.valueOf()
   const MAX_INT = 2147483647
   const MIN_INT = -2147483648
   return (timestamp === timestamp && timestamp <= MAX_INT && timestamp >= MIN_INT) // eslint-disable-line
diff --git a/yarn.lock b/yarn.lock
index dba4432..68f68ec 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1889,9 +1889,10 @@ flat-cache@^1.2.1:
     graceful-fs "^4.1.2"
     write "^0.2.1"
 
-flow-bin@^0.81.0:
-  version "0.81.0"
-  resolved "https://registry.yarnpkg.com/flow-bin/-/flow-bin-0.81.0.tgz#7f0a733dce1dad3cb1447c692639292dc3d60bf5"
+flow-bin@^0.107.0:
+  version "0.107.0"
+  resolved "https://registry.yarnpkg.com/flow-bin/-/flow-bin-0.107.0.tgz#b37bfcce51204d35d58f8eb93b3a76b52291e4cc"
+  integrity sha512-hsmwO5Q0+XUXaO2kIKLpleUNNBSFcsGEQGBOTEC/KR/4Ez695I1fweX/ioSjbU4RWhPZhkIqnpbF9opVAauCHg==
 
 for-in@^0.1.5:
   version "0.1.6"
@@ -2108,9 +2109,10 @@ graceful-fs@^4.1.11, graceful-fs@^4.1.2, graceful-fs@^4.1.4:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/graceful-readlink/-/graceful-readlink-1.0.1.tgz#4cafad76bc62f02fa039b2f94e9a3dd3a391a725"
 
-graphql@^14.0.2:
-  version "14.0.2"
-  resolved "https://registry.yarnpkg.com/graphql/-/graphql-14.0.2.tgz#7dded337a4c3fd2d075692323384034b357f5650"
+graphql@^14.2.1:
+  version "14.2.1"
+  resolved "https://registry.yarnpkg.com/graphql/-/graphql-14.2.1.tgz#779529bf9a01e7207b977a54c20670b48ca6e95c"
+  integrity sha512-2PL1UbvKeSjy/lUeJqHk+eR9CvuErXoCNwJI4jm3oNFEeY+9ELqHNKO1ZuSxAkasPkpWbmT/iMRMFxd3cEL3tQ==
   dependencies:
     iterall "^1.2.2"