diff --git a/test/built-ins/BigInt/prototype/toString/length.js b/test/built-ins/BigInt/prototype/toString/length.js
new file mode 100644
index 0000000000..b5cc5fb399
--- /dev/null
+++ b/test/built-ins/BigInt/prototype/toString/length.js
@@ -0,0 +1,19 @@
+// Copyright (C) 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.tostring
+description: BigInt.prototype.toString.length property descriptor
+info: >
+  BigInt.prototype.toString ( [ radix ] )
+
+  17 ECMAScript Standard Built-in Objects
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(BigInt.prototype.toString, "length", {
+  value: 1,
+  writable: false,
+  enumerable: false,
+  configurable: true
+});
diff --git a/test/built-ins/BigInt/prototype/toString/name.js b/test/built-ins/BigInt/prototype/toString/name.js
new file mode 100644
index 0000000000..f78ba20c46
--- /dev/null
+++ b/test/built-ins/BigInt/prototype/toString/name.js
@@ -0,0 +1,19 @@
+// Copyright (C) 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.tostring
+description: BigInt.prototype.toString.name property descriptor
+info: >
+  BigInt.prototype.toString ( [ radix ] )
+
+  17 ECMAScript Standard Built-in Objects
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(BigInt.prototype.toString, "name", {
+  value: "toString",
+  writable: false,
+  enumerable: false,
+  configurable: true
+});
diff --git a/test/built-ins/BigInt/prototype/toString/non-bigint.js b/test/built-ins/BigInt/prototype/toString/non-bigint.js
new file mode 100644
index 0000000000..761cec1c33
--- /dev/null
+++ b/test/built-ins/BigInt/prototype/toString/non-bigint.js
@@ -0,0 +1,16 @@
+// Copyright 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.tostring
+description: Transferring toString to non-BigInt objects
+info: >
+  BigInt.prototype.toString ( [ radix ] )
+
+  1. Let x be ? thisBigIntValue(this value).
+---*/
+
+for (let x of [new String(), new Boolean(), new Date(), new Object(), {x: 1}]) {
+  x.toString = Number.prototype.toString;
+  assert.throws(TypeError, () => x.toString());
+}
diff --git a/test/built-ins/BigInt/prototype/toString/prop-desc.js b/test/built-ins/BigInt/prototype/toString/prop-desc.js
new file mode 100644
index 0000000000..b9840050e5
--- /dev/null
+++ b/test/built-ins/BigInt/prototype/toString/prop-desc.js
@@ -0,0 +1,18 @@
+// Copyright (C) 2016 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.tostring
+description: BigInt.prototype.toString property descriptor
+info: >
+  BigInt.prototype.toString ( [ radix ] )
+
+  17 ECMAScript Standard Built-in Objects
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(BigInt.prototype, "toString", {
+  writable: true,
+  enumerable: false,
+  configurable: true
+});
diff --git a/test/built-ins/BigInt/prototype/toString/prototype-call.js b/test/built-ins/BigInt/prototype/toString/prototype-call.js
new file mode 100644
index 0000000000..ae2b0e8cd9
--- /dev/null
+++ b/test/built-ins/BigInt/prototype/toString/prototype-call.js
@@ -0,0 +1,20 @@
+// Copyright 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.tostring
+description: Direct toString on BigInt prototype
+info: >
+  BigInt.prototype.toString ( [ radix ] )
+
+  Let x be ? thisBigIntValue(this value).
+
+  Properties of the BigInt Prototype Object
+
+  The BigInt prototype is not a BigInt object; it does not have a
+  [[BigIntData]] internal slot.
+---*/
+
+assert.throws(TypeError, () => BigInt.prototype.toString());
+assert.throws(TypeError, () => BigInt.prototype.toString(10));
+assert.throws(TypeError, () => BigInt.prototype.toString(undefined));
diff --git a/test/built-ins/BigInt/prototype/toString/radix-2-to-36.js b/test/built-ins/BigInt/prototype/toString/radix-2-to-36.js
new file mode 100644
index 0000000000..e03eb66d73
--- /dev/null
+++ b/test/built-ins/BigInt/prototype/toString/radix-2-to-36.js
@@ -0,0 +1,24 @@
+// Copyright 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.tostring
+description: toString with radix between 2 and 36
+info: >
+  BigInt.prototype.toString ( [ radix ] )
+
+  [...]
+  6. If radixNumber = 10, return ! ToString(x).
+  7. Return the String representation of this Number value using the
+     radix specified by radixNumber. Letters a-z are used for digits
+     with values 10 through 35. The precise algorithm is
+     implementation-dependent, however the algorithm should be a
+     generalization of that specified in 3.1.4.1.
+---*/
+
+for (let r = 2; r <= 36; r++) {
+  assert.throws(TypeError, () => BigInt.prototype.toString(r));
+  assert.sameValue((0n).toString(r), "0", "0, radix " + r);
+  assert.sameValue((-1n).toString(r), "-1", "-1, radix " + r);
+  assert.sameValue((1n).toString(r), "1", "1, radix " + r);
+}
diff --git a/test/built-ins/BigInt/prototype/toString/radix-err.js b/test/built-ins/BigInt/prototype/toString/radix-err.js
new file mode 100644
index 0000000000..18d6574a31
--- /dev/null
+++ b/test/built-ins/BigInt/prototype/toString/radix-err.js
@@ -0,0 +1,21 @@
+// Copyright 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.tostring
+description: toString with invalid radix
+info: >
+  BigInt.prototype.toString ( [ radix ] )
+
+  [...]
+  4. Else, let radixNumber be ? ToInteger(radix).
+  5. If radixNumber < 2 or radixNumber > 36, throw a RangeError
+     exception.
+---*/
+
+for (let r of [0, 1, 37, null]) {
+  assert.throws(TypeError, () => BigInt.prototype.toString(r));
+  assert.throws(RangeError, () => (0n).toString(r), "0, radix " + r);
+  assert.throws(RangeError, () => (-1n).toString(r), "-1, radix " + r);
+  assert.throws(RangeError, () => (1n).toString(r), "1, radix " + r);
+}