diff --git a/test/intl402/NumberFormat/prototype/format/default-value.js b/test/intl402/NumberFormat/prototype/format/default-value.js
index 54a9996d6a..a8eb83d91a 100644
--- a/test/intl402/NumberFormat/prototype/format/default-value.js
+++ b/test/intl402/NumberFormat/prototype/format/default-value.js
@@ -7,11 +7,17 @@ description: >
   Tests that the default value for the argument of
   Intl.NumberFormat.prototype.format (value) is undefined.
 info: |
-  11.1.4Number Format Functions
+  11.1.4 Number Format Functions
 
   3. If value is not provided, let value be undefined.
+  4. Let x be ? ToNumber(value).
 ---*/
 
 const nf = new Intl.NumberFormat();
-assert.sameValue(nf.format(), NaN);
-assert.sameValue(nf.format(undefined), NaN);
+
+// In most locales this is string "NaN", but there are exceptions, cf. "ليس رقم"
+// in Arabic, "epäluku" in Finnish, "не число" in Russian, "son emas" in Uzbek etc.
+const resultNaN = nf.format(NaN);
+
+assert.sameValue(nf.format(), resultNaN);
+assert.sameValue(nf.format(undefined), resultNaN);
diff --git a/test/intl402/NumberFormat/prototype/format/this-value-not-numberformat.js b/test/intl402/NumberFormat/prototype/format/this-value-not-numberformat.js
index 3e7cb30772..1b83c3368f 100644
--- a/test/intl402/NumberFormat/prototype/format/this-value-not-numberformat.js
+++ b/test/intl402/NumberFormat/prototype/format/this-value-not-numberformat.js
@@ -16,6 +16,6 @@ invalidTargets.forEach(target => {
   assert.throws(
     TypeError,
     () => fn.call(target),
-    `Calling format getter on ${target} should throw a TypeError.`
+    `Calling format getter on ${String(target)} should throw a TypeError.`
   );
 });
diff --git a/test/intl402/NumberFormat/prototype/formatToParts/this-value-not-numberformat.js b/test/intl402/NumberFormat/prototype/formatToParts/this-value-not-numberformat.js
index 3e095893ea..ea60ed023b 100644
--- a/test/intl402/NumberFormat/prototype/formatToParts/this-value-not-numberformat.js
+++ b/test/intl402/NumberFormat/prototype/formatToParts/this-value-not-numberformat.js
@@ -16,6 +16,6 @@ invalidTargets.forEach(target => {
   assert.throws(
     TypeError,
     () => fn.call(target),
-    `Calling formatToParts on ${target} should throw a TypeError.`
+    `Calling formatToParts on ${String(target)} should throw a TypeError.`
   );
 });
diff --git a/test/intl402/NumberFormat/prototype/resolvedOptions/this-value-not-numberformat.js b/test/intl402/NumberFormat/prototype/resolvedOptions/this-value-not-numberformat.js
index 28f41cf54c..bc72bf7bc6 100644
--- a/test/intl402/NumberFormat/prototype/resolvedOptions/this-value-not-numberformat.js
+++ b/test/intl402/NumberFormat/prototype/resolvedOptions/this-value-not-numberformat.js
@@ -16,6 +16,6 @@ invalidTargets.forEach(target => {
   assert.throws(
     TypeError,
     () => fn.call(target),
-    `Calling resolvedOptions on ${target} should throw a TypeError.`
+    `Calling resolvedOptions on ${String(target)} should throw a TypeError.`
   );
 });