diff --git a/src/LuaLib.ts b/src/LuaLib.ts
index c877dd9cc..b50ab1e75 100644
--- a/src/LuaLib.ts
+++ b/src/LuaLib.ts
@@ -40,6 +40,7 @@ export enum LuaLibFeature {
     Number = "Number",
     NumberIsFinite = "NumberIsFinite",
     NumberIsNaN = "NumberIsNaN",
+    NumberToString = "NumberToString",
     ObjectAssign = "ObjectAssign",
     ObjectEntries = "ObjectEntries",
     ObjectFromEntries = "ObjectFromEntries",
diff --git a/src/LuaTransformer.ts b/src/LuaTransformer.ts
index e460993b7..5479fc889 100644
--- a/src/LuaTransformer.ts
+++ b/src/LuaTransformer.ts
@@ -4295,7 +4295,7 @@ export class LuaTransformer {
         }
 
         if (tsHelper.isStandardLibraryType(ownerType, "NumberConstructor", this.program)) {
-            return this.transformNumberCallExpression(node);
+            return this.transformNumberExpression(node);
         }
 
         const classDecorators = tsHelper.getCustomDecorators(ownerType, this.checker);
@@ -4308,6 +4308,10 @@ export class LuaTransformer {
             return this.transformStringCallExpression(node);
         }
 
+        if (tsHelper.isNumberType(ownerType, this.checker, this.program)) {
+            return this.transformNumberCallExpression(node);
+        }
+
         // if ownerType is a array, use only supported functions
         if (tsHelper.isExplicitArrayType(ownerType, this.checker, this.program)) {
             return this.transformArrayCallExpression(node);
@@ -4883,6 +4887,23 @@ export class LuaTransformer {
         );
     }
 
+    protected transformNumberCallExpression(node: ts.CallExpression): tstl.Expression {
+        const expression = node.expression as ts.PropertyAccessExpression;
+        const signature = this.checker.getResolvedSignature(node);
+        const params = this.transformArguments(node.arguments, signature);
+        const caller = this.transformExpression(expression.expression);
+
+        const expressionName = expression.name.text;
+        switch (expressionName) {
+            case "toString":
+                return params.length === 0
+                    ? tstl.createCallExpression(tstl.createIdentifier("tostring"), [caller], node)
+                    : this.transformLuaLibFunction(LuaLibFeature.NumberToString, node, caller, ...params);
+            default:
+                throw TSTLErrors.UnsupportedProperty("number", expressionName, node);
+        }
+    }
+
     // Transpile a String._ property
     protected transformStringExpression(identifier: ts.Identifier): ExpressionVisitResult {
         const identifierString = identifier.text;
@@ -5015,7 +5036,7 @@ export class LuaTransformer {
     }
 
     // Transpile a Number._ property
-    protected transformNumberCallExpression(expression: ts.CallExpression): tstl.CallExpression {
+    protected transformNumberExpression(expression: ts.CallExpression): tstl.CallExpression {
         const method = expression.expression as ts.PropertyAccessExpression;
         const parameters = this.transformArguments(expression.arguments);
         const methodName = method.name.text;
diff --git a/src/lualib/NumberToString.ts b/src/lualib/NumberToString.ts
new file mode 100644
index 000000000..3ad9a3d5e
--- /dev/null
+++ b/src/lualib/NumberToString.ts
@@ -0,0 +1,49 @@
+// tslint:disable-next-line: variable-name
+const ____radixChars = "0123456789abcdefghijklmnopqrstuvwxyz";
+
+// https://www.ecma-international.org/ecma-262/10.0/index.html#sec-number.prototype.tostring
+function __TS__NumberToString(this: number, radix?: number): string {
+    if (radix === undefined || radix === 10 || this === Infinity || this === -Infinity || this !== this) {
+        return this.toString();
+    }
+
+    radix = Math.floor(radix);
+    if (radix < 2 || radix > 36) {
+        // tslint:disable-next-line: no-string-throw
+        throw "toString() radix argument must be between 2 and 36";
+    }
+
+    let [integer, fraction] = math.modf(Math.abs(this));
+
+    let result = "";
+    if (radix === 8) {
+        result = string.format("%o", integer);
+    } else if (radix === 16) {
+        result = string.format("%x", integer);
+    } else {
+        do {
+            result = ____radixChars[integer % radix] + result;
+            integer = Math.floor(integer / radix);
+        } while (integer !== 0);
+    }
+
+    // https://github.com/v8/v8/blob/f78e8d43c224847fa56b3220a90be250fc0f0d6e/src/numbers/conversions.cc#L1221
+    if (fraction !== 0) {
+        result += ".";
+        let delta = 1e-16;
+        do {
+            fraction *= radix;
+            delta *= radix;
+            const digit = Math.floor(fraction);
+            result += ____radixChars[digit];
+            fraction -= digit;
+            // TODO: Round to even
+        } while (fraction >= delta);
+    }
+
+    if (this < 0) {
+        result = "-" + result;
+    }
+
+    return result;
+}
diff --git a/src/lualib/declarations/math.d.ts b/src/lualib/declarations/math.d.ts
new file mode 100644
index 000000000..a0fb6c0e6
--- /dev/null
+++ b/src/lualib/declarations/math.d.ts
@@ -0,0 +1,5 @@
+/** @noSelf */
+declare namespace math {
+    /** @tupleReturn */
+    function modf(x: number): [number, number];
+}
diff --git a/src/lualib/declarations/string.d.ts b/src/lualib/declarations/string.d.ts
index 1003f5450..a21500d28 100644
--- a/src/lualib/declarations/string.d.ts
+++ b/src/lualib/declarations/string.d.ts
@@ -8,4 +8,5 @@ declare namespace string {
         n?: number
     ): [string, number];
     function sub(s: string, i: number, j?: number): string;
+    function format(formatstring: string, ...args: any[]): string;
 }
diff --git a/src/utils.ts b/src/utils.ts
index 0fe3f68b6..204a1d16c 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -1 +1,16 @@
 export const normalizeSlashes = (filePath: string) => filePath.replace(/\\/g, "/");
+
+export function flatMap<T, U>(array: readonly T[], callback: (value: T, index: number) => U | readonly U[]): U[] {
+    const result: U[] = [];
+
+    for (const [index, value] of array.entries()) {
+        const mappedValue = callback(value, index);
+        if (Array.isArray(mappedValue)) {
+            result.push(...mappedValue);
+        } else {
+            result[result.length] = mappedValue as U;
+        }
+    }
+
+    return result;
+}
diff --git a/test/unit/builtins/numbers.spec.ts b/test/unit/builtins/numbers.spec.ts
index 4369f22c6..7a5d5c731 100644
--- a/test/unit/builtins/numbers.spec.ts
+++ b/test/unit/builtins/numbers.spec.ts
@@ -1,3 +1,4 @@
+import { flatMap } from "../../../src/utils";
 import * as util from "../../util";
 
 test.each([
@@ -48,6 +49,18 @@ describe("Number", () => {
     });
 });
 
+const toStringRadixes = [undefined, 10, 2, 8, 9, 16, 17, 36, 36.9];
+const toStringValues = [-1, 0, 1, 1.5, 1024, 1.2];
+const toStringPairs = flatMap(toStringValues, value => toStringRadixes.map(radix => [value, radix] as const));
+
+test.each(toStringPairs)("(%p).toString(%p)", (value, radix) => {
+    util.testExpressionTemplate`(${value}).toString(${radix})`.expectToMatchJsResult();
+});
+
+test.each([NaN, Infinity, -Infinity])("%p.toString(2)", value => {
+    util.testExpressionTemplate`(${value}).toString(2)`.expectToMatchJsResult();
+});
+
 test.each(cases)("isNaN(%p)", value => {
     util.testExpressionTemplate`isNaN(${value} as any)`.expectToMatchJsResult();
 });