diff --git a/test/intl402/RelativeTimeFormat/prototype/format/value-tonumber.js b/test/intl402/RelativeTimeFormat/prototype/format/value-tonumber.js
new file mode 100644
index 0000000000..c951ed3d5a
--- /dev/null
+++ b/test/intl402/RelativeTimeFormat/prototype/format/value-tonumber.js
@@ -0,0 +1,38 @@
+// Copyright 2018 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-Intl.RelativeTimeFormat.prototype.format
+description: Checks the handling of non-number value arguments to Intl.RelativeTimeFormat.prototype.format().
+info: |
+    Intl.RelativeTimeFormat.prototype.format( value, unit )
+
+    3. Let value be ? ToNumber(value).
+
+features: [Intl.RelativeTimeFormat]
+---*/
+
+const rtf = new Intl.RelativeTimeFormat("en-US");
+
+assert.sameValue(typeof rtf.format, "function", "format should be supported");
+
+const values = [
+  [null, 0],
+
+  [true, 1],
+  [false, 0],
+
+  ["5", 5],
+  ["-5", -5],
+  ["0", 0],
+  ["-0", -0],
+  ["  6  ", 6],
+
+  [{ toString() { return 7; } }, 7, "object with toString"],
+  [{ valueOf() { return 7; } }, 7, "object with valueOf"],
+];
+
+for (const [input, number, name = String(input)] of values) {
+  assert.sameValue(rtf.format(input, "second"), rtf.format(number, "second"),
+                   `Should treat ${name} as ${number}`)
+}
diff --git a/test/intl402/RelativeTimeFormat/prototype/formatToParts/value-tonumber.js b/test/intl402/RelativeTimeFormat/prototype/formatToParts/value-tonumber.js
new file mode 100644
index 0000000000..c82b072e85
--- /dev/null
+++ b/test/intl402/RelativeTimeFormat/prototype/formatToParts/value-tonumber.js
@@ -0,0 +1,50 @@
+// Copyright 2018 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-Intl.RelativeTimeFormat.prototype.format
+description: Checks the handling of non-number value arguments to Intl.RelativeTimeFormat.prototype.format().
+info: |
+    Intl.RelativeTimeFormat.prototype.format( value, unit )
+
+    3. Let value be ? ToNumber(value).
+
+features: [Intl.RelativeTimeFormat]
+---*/
+
+const rtf = new Intl.RelativeTimeFormat("en-US");
+
+assert.sameValue(typeof rtf.format, "function", "format should be supported");
+
+const values = [
+  [null, 0],
+
+  [true, 1],
+  [false, 0],
+
+  ["5", 5],
+  ["-5", -5],
+  ["0", 0],
+  ["-0", -0],
+  ["  6  ", 6],
+
+  [{ toString() { return 7; } }, 7, "object with toString"],
+  [{ valueOf() { return 7; } }, 7, "object with valueOf"],
+];
+
+for (const [input, number, name = String(input)] of values) {
+  const actual = rtf.formatToParts(input, "second");
+  const expected = rtf.formatToParts(number, "second");
+
+  assert.sameValue(actual.length, expected.length,
+                   `Should treat ${name} as ${number}: length`);
+
+  for (let i = 0; i < actual.length; ++i) {
+    assert.sameValue(actual[i].type, expected[i].type,
+                     `Should treat ${name} as ${number}: [${i}].type`);
+    assert.sameValue(actual[i].value, expected[i].value,
+                     `Should treat ${name} as ${number}: [${i}].value`);
+    assert.sameValue(actual[i].unit, expected[i].unit,
+                     `Should treat ${name} as ${number}: [${i}].unit`);
+  }
+}