diff --git a/test/built-ins/Array/prototype/join/number-elements.js b/test/built-ins/Array/prototype/join/number-elements.js
new file mode 100644
index 00000000000..7a8c10d3c6a
--- /dev/null
+++ b/test/built-ins/Array/prototype/join/number-elements.js
@@ -0,0 +1,97 @@
+// Copyright (C) 2026 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-array.prototype.join
+description: >
+  Number elements are joined correctly, including digit-count and 32-bit
+  boundaries, non-integers, and very large and small values
+---*/
+
+var cases = [
+  [0, "0"],
+  [1, "1"],
+  [-1, "-1"],
+  [2147483647, "2147483647"],
+  [-2147483647, "-2147483647"],
+  [-2147483648, "-2147483648"],
+  [2147483648, "2147483648"],
+  [-2147483649, "-2147483649"],
+  [4294967295, "4294967295"],
+  [-4294967295, "-4294967295"],
+  [4294967296, "4294967296"],
+  [-4294967296, "-4294967296"],
+  [9007199254740991, "9007199254740991"],
+  [-9007199254740991, "-9007199254740991"],
+  [9007199254740992, "9007199254740992"],
+  [100000000000000000000, "100000000000000000000"],
+  [999999999999999900000, "999999999999999900000"],
+  [9, "9"],
+  [10, "10"],
+  [99, "99"],
+  [100, "100"],
+  [999, "999"],
+  [1000, "1000"],
+  [9999, "9999"],
+  [10000, "10000"],
+  [99999, "99999"],
+  [100000, "100000"],
+  [999999, "999999"],
+  [1000000, "1000000"],
+  [9999999, "9999999"],
+  [10000000, "10000000"],
+  [99999999, "99999999"],
+  [100000000, "100000000"],
+  [999999999, "999999999"],
+  [1000000000, "1000000000"],
+  [9999999999, "9999999999"],
+  [10000000000, "10000000000"],
+  [99999999999, "99999999999"],
+  [100000000000, "100000000000"],
+  [999999999999, "999999999999"],
+  [1000000000000, "1000000000000"],
+  [9999999999999, "9999999999999"],
+  [10000000000000, "10000000000000"],
+  [99999999999999, "99999999999999"],
+  [100000000000000, "100000000000000"],
+  [999999999999999, "999999999999999"],
+  [-0, "0"],
+  [0.1, "0.1"],
+  [-0.1, "-0.1"],
+  [1.5, "1.5"],
+  [-1.5, "-1.5"],
+  [0.1 + 0.2, "0.30000000000000004"],
+  [123456789.125, "123456789.125"],
+  [2147483647.5, "2147483647.5"],
+  [-2147483648.5, "-2147483648.5"],
+  [0.000001, "0.000001"],
+  [0.000001234, "0.000001234"],
+  [1e-7, "1e-7"],
+  [-1e-7, "-1e-7"],
+  [1.25e-7, "1.25e-7"],
+  [123e-20, "1.23e-18"],
+  [1e21, "1e+21"],
+  [-1e21, "-1e+21"],
+  [1.5e300, "1.5e+300"],
+  [5e-324, "5e-324"],
+  [-5e-324, "-5e-324"],
+  [2.2250738585072014e-308, "2.2250738585072014e-308"],
+  [-2.2250738585072014e-308, "-2.2250738585072014e-308"],
+  [1.7976931348623157e308, "1.7976931348623157e+308"],
+  [-1.7976931348623157e308, "-1.7976931348623157e+308"],
+  [NaN, "NaN"],
+  [Infinity, "Infinity"],
+  [-Infinity, "-Infinity"],
+];
+
+for (var i = 0; i < cases.length; i++) {
+  var value = cases[i][0];
+  var expected = cases[i][1];
+
+  assert.sameValue([value].join(), expected, "single element: " + expected);
+  assert.sameValue([value, value].join(), expected + "," + expected,
+    "default separator: " + expected);
+  assert.sameValue([value, value].join(""), expected + expected,
+    "empty separator: " + expected);
+  assert.sameValue([value, value].join("—"), expected + "—" + expected,
+    "non-Latin-1 separator: " + expected);
+}
diff --git a/test/built-ins/JSON/stringify/value-number.js b/test/built-ins/JSON/stringify/value-number.js
new file mode 100644
index 00000000000..5dab3d8061a
--- /dev/null
+++ b/test/built-ins/JSON/stringify/value-number.js
@@ -0,0 +1,96 @@
+// Copyright (C) 2026 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-json.stringify
+description: >
+  Number values are serialized correctly, including digit-count and
+  32-bit boundaries, non-integers, and very large and small values
+---*/
+
+var cases = [
+  [0, "0"],
+  [1, "1"],
+  [-1, "-1"],
+  [2147483647, "2147483647"],
+  [-2147483647, "-2147483647"],
+  [-2147483648, "-2147483648"],
+  [2147483648, "2147483648"],
+  [-2147483649, "-2147483649"],
+  [4294967295, "4294967295"],
+  [-4294967295, "-4294967295"],
+  [4294967296, "4294967296"],
+  [-4294967296, "-4294967296"],
+  [9007199254740991, "9007199254740991"],
+  [-9007199254740991, "-9007199254740991"],
+  [9007199254740992, "9007199254740992"],
+  [100000000000000000000, "100000000000000000000"],
+  [999999999999999900000, "999999999999999900000"],
+  [9, "9"],
+  [10, "10"],
+  [99, "99"],
+  [100, "100"],
+  [999, "999"],
+  [1000, "1000"],
+  [9999, "9999"],
+  [10000, "10000"],
+  [99999, "99999"],
+  [100000, "100000"],
+  [999999, "999999"],
+  [1000000, "1000000"],
+  [9999999, "9999999"],
+  [10000000, "10000000"],
+  [99999999, "99999999"],
+  [100000000, "100000000"],
+  [999999999, "999999999"],
+  [1000000000, "1000000000"],
+  [9999999999, "9999999999"],
+  [10000000000, "10000000000"],
+  [99999999999, "99999999999"],
+  [100000000000, "100000000000"],
+  [999999999999, "999999999999"],
+  [1000000000000, "1000000000000"],
+  [9999999999999, "9999999999999"],
+  [10000000000000, "10000000000000"],
+  [99999999999999, "99999999999999"],
+  [100000000000000, "100000000000000"],
+  [999999999999999, "999999999999999"],
+  [0.1, "0.1"],
+  [-0.1, "-0.1"],
+  [1.5, "1.5"],
+  [-1.5, "-1.5"],
+  [0.1 + 0.2, "0.30000000000000004"],
+  [123456789.125, "123456789.125"],
+  [2147483647.5, "2147483647.5"],
+  [-2147483648.5, "-2147483648.5"],
+  [0.000001, "0.000001"],
+  [0.000001234, "0.000001234"],
+  [1e-7, "1e-7"],
+  [-1e-7, "-1e-7"],
+  [1.25e-7, "1.25e-7"],
+  [123e-20, "1.23e-18"],
+  [1e21, "1e+21"],
+  [-1e21, "-1e+21"],
+  [1.5e300, "1.5e+300"],
+  [5e-324, "5e-324"],
+  [-5e-324, "-5e-324"],
+  [2.2250738585072014e-308, "2.2250738585072014e-308"],
+  [-2.2250738585072014e-308, "-2.2250738585072014e-308"],
+  [1.7976931348623157e308, "1.7976931348623157e+308"],
+  [-1.7976931348623157e308, "-1.7976931348623157e+308"],
+];
+
+for (var i = 0; i < cases.length; i++) {
+  var value = cases[i][0];
+  var expected = cases[i][1];
+
+  assert.sameValue(JSON.stringify(value), expected, "top level: " + expected);
+  assert.sameValue(JSON.stringify([value]), "[" + expected + "]",
+    "array element: " + expected);
+  assert.sameValue(JSON.stringify([value, value]),
+    "[" + expected + "," + expected + "]", "array elements: " + expected);
+  assert.sameValue(JSON.stringify({ key: value }), '{"key":' + expected + "}",
+    "property value: " + expected);
+  assert.sameValue(JSON.stringify({ a: [value], b: { c: value } }),
+    '{"a":[' + expected + '],"b":{"c":' + expected + "}}",
+    "nested: " + expected);
+}