diff --git a/src/polyfills/isFinite.js b/src/polyfills/isFinite.js
deleted file mode 100644
index 58f8614b9f..0000000000
--- a/src/polyfills/isFinite.js
+++ /dev/null
@@ -1,12 +0,0 @@
-declare function isFinitePolyfill(
-  value: mixed,
-): boolean %checks(typeof value === 'number');
-
-/* eslint-disable no-redeclare */
-// $FlowFixMe[name-already-bound] workaround for: https://github.com/facebook/flow/issues/4441
-const isFinitePolyfill =
-  Number.isFinite ||
-  function (value) {
-    return typeof value === 'number' && isFinite(value);
-  };
-export default isFinitePolyfill;
diff --git a/src/polyfills/isInteger.js b/src/polyfills/isInteger.js
deleted file mode 100644
index fdd50ff247..0000000000
--- a/src/polyfills/isInteger.js
+++ /dev/null
@@ -1,15 +0,0 @@
-declare function isInteger(value: mixed): boolean %checks(typeof value ===
-  'number');
-
-/* eslint-disable no-redeclare */
-// $FlowFixMe[name-already-bound] workaround for: https://github.com/facebook/flow/issues/4441
-const isInteger =
-  Number.isInteger ||
-  function (value) {
-    return (
-      typeof value === 'number' &&
-      isFinite(value) &&
-      Math.floor(value) === value
-    );
-  };
-export default isInteger;
diff --git a/src/type/scalars.js b/src/type/scalars.js
index ceca14b5c3..e02d2e5c6c 100644
--- a/src/type/scalars.js
+++ b/src/type/scalars.js
@@ -1,6 +1,3 @@
-import isFinite from '../polyfills/isFinite';
-import isInteger from '../polyfills/isInteger';
-
 import inspect from '../jsutils/inspect';
 import isObjectLike from '../jsutils/isObjectLike';
 
@@ -32,7 +29,7 @@ function serializeInt(outputValue: mixed): number {
     num = Number(coercedValue);
   }
 
-  if (!isInteger(num)) {
+  if (typeof num !== 'number' || !Number.isInteger(num)) {
     throw new GraphQLError(
       `Int cannot represent non-integer value: ${inspect(coercedValue)}`,
     );
@@ -47,7 +44,7 @@ function serializeInt(outputValue: mixed): number {
 }
 
 function coerceInt(inputValue: mixed): number {
-  if (!isInteger(inputValue)) {
+  if (typeof inputValue !== 'number' || !Number.isInteger(inputValue)) {
     throw new GraphQLError(
       `Int cannot represent non-integer value: ${inspect(inputValue)}`,
     );
@@ -96,7 +93,7 @@ function serializeFloat(outputValue: mixed): number {
     num = Number(coercedValue);
   }
 
-  if (!isFinite(num)) {
+  if (typeof num !== 'number' || !Number.isFinite(num)) {
     throw new GraphQLError(
       `Float cannot represent non numeric value: ${inspect(coercedValue)}`,
     );
@@ -105,7 +102,7 @@ function serializeFloat(outputValue: mixed): number {
 }
 
 function coerceFloat(inputValue: mixed): number {
-  if (!isFinite(inputValue)) {
+  if (typeof inputValue !== 'number' || !Number.isFinite(inputValue)) {
     throw new GraphQLError(
       `Float cannot represent non numeric value: ${inspect(inputValue)}`,
     );
@@ -160,7 +157,7 @@ function serializeString(outputValue: mixed): string {
   if (typeof coercedValue === 'boolean') {
     return coercedValue ? 'true' : 'false';
   }
-  if (isFinite(coercedValue)) {
+  if (typeof coercedValue === 'number' && Number.isFinite(coercedValue)) {
     return coercedValue.toString();
   }
   throw new GraphQLError(
@@ -200,7 +197,7 @@ function serializeBoolean(outputValue: mixed): boolean {
   if (typeof coercedValue === 'boolean') {
     return coercedValue;
   }
-  if (isFinite(coercedValue)) {
+  if (Number.isFinite(coercedValue)) {
     return coercedValue !== 0;
   }
   throw new GraphQLError(
@@ -239,7 +236,7 @@ function serializeID(outputValue: mixed): string {
   if (typeof coercedValue === 'string') {
     return coercedValue;
   }
-  if (isInteger(coercedValue)) {
+  if (Number.isInteger(coercedValue)) {
     return String(coercedValue);
   }
   throw new GraphQLError(`ID cannot represent value: ${inspect(outputValue)}`);
@@ -249,7 +246,7 @@ function coerceID(inputValue: mixed): string {
   if (typeof inputValue === 'string') {
     return inputValue;
   }
-  if (isInteger(inputValue)) {
+  if (typeof inputValue === 'number' && Number.isInteger(inputValue)) {
     return inputValue.toString();
   }
   throw new GraphQLError(`ID cannot represent value: ${inspect(inputValue)}`);
diff --git a/src/utilities/astFromValue.js b/src/utilities/astFromValue.js
index 39ab089d27..eb63cadeea 100644
--- a/src/utilities/astFromValue.js
+++ b/src/utilities/astFromValue.js
@@ -1,4 +1,3 @@
-import isFinite from '../polyfills/isFinite';
 import arrayFrom from '../polyfills/arrayFrom';
 import objectValues from '../polyfills/objectValues';
 
@@ -114,7 +113,7 @@ export function astFromValue(value: mixed, type: GraphQLInputType): ?ValueNode {
     }
 
     // JavaScript numbers can be Int or Float values.
-    if (typeof serialized === 'number' && isFinite(serialized)) {
+    if (typeof serialized === 'number' && Number.isFinite(serialized)) {
       const stringNum = String(serialized);
       return integerStringRegExp.test(stringNum)
         ? { kind: Kind.INT, value: stringNum }