diff --git a/CHANGELOG.md b/CHANGELOG.md
index 527a87d..e08c746 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -58,6 +58,7 @@ QueryPath Changelog
 - Consolidate the sibling and ancestor walks behind `next()`, `prev()`, `nextAll()`, `prevAll()`, `nextUntil()`, `prevUntil()`, `parent()`, `parents()`, `parentsUntil()` and `closest()` into one helper, so a fix to one no longer has to be repeated in its mirror (issue #115). As a side effect, `parentsUntil()` no longer loops forever on an element that is not attached to the document, and `nextUntil('')` and `prevUntil('')` treat an empty selector as no selector, as the other methods already did, instead of throwing `QueryPath\CSS\ParseException`. `closest('')` returns an empty set, as in jQuery. `nextUntil()`, `prevUntil()` and `parentsUntil()` also stop at an element already collected from an earlier starting element, as `nextAll()` and `prevAll()` do, so `nextUntil()` on each of 2000 siblings falls from about 100 ms to 1 ms
 - **Behaviour change.** `prevAll()`, `prevUntil()`, `nextAll()`, `nextUntil()`, `siblings()`, `parent()` and `closest()` now return the results for a multi-element set in jQuery's order, instead of grouped by starting element (issue #117). `prevAll()` and `prevUntil()` return reverse document order, as `parents()` and `parentsUntil()` already did, and the others return document order. `qp($xml, 'c')->add('d')->prevAll()` now returns `c, b, a` rather than `b, a, c`. `next()` and `prev()` keep the order of the starting elements, as in jQuery, and the results for a single starting element are unchanged
 - **Behaviour change.** A positional pseudo-class (`:first`, `:eq()`, `:last`, ...) in the stop selector of `nextUntil()`, `prevUntil()` and `parentsUntil()` now counts across the whole document, as jQuery's does, instead of seeing each sibling or ancestor as a one-element set (issue #118). `nextUntil(':first')` used to stop at once and now walks to the end, and `nextUntil(':eq(3)')` stops at the fourth element in the document. `closest()` no longer matches a positional selector at all, as in jQuery, where `closest(':first')` used to return the element itself. `next()`, `prev()` and `parent()` still test each candidate on its own, which agrees with jQuery for a single starting element
+- Add `:is()` and `:where()` as aliases of `:matches()` (issue #136). QueryPath doesn't use specificity, so `:where()` matches exactly as `:is()` does, and a positional argument (`:is(:first)`) is applied to the whole set as it is for `:matches()`
 
 # 4.2.0
 
diff --git a/src/CSS/DOMTraverser/PseudoClass.php b/src/CSS/DOMTraverser/PseudoClass.php
index 5815aed..adc096d 100644
--- a/src/CSS/DOMTraverser/PseudoClass.php
+++ b/src/CSS/DOMTraverser/PseudoClass.php
@@ -261,6 +261,8 @@ public function elementMatches($pseudoclass, $node, $scope, $value = null)
 			case 'has':
 				return $this->has($node, $value);
 			case 'matches':
+			case 'is':
+			case 'where':
 				return $this->is($node, $value);
 			case 'not':
 				if (empty($value)) {
@@ -541,7 +543,7 @@ protected function findsAny(DOMElement $root, DOMElement $scope, array $group, b
 	}
 
 	/**
-	 * Provides :matches pseudoclass, which tests the node itself.
+	 * Provides :matches pseudoclass (and its :is and :where aliases), which tests the node itself.
 	 *
 	 * @throws ParseException
 	 */
diff --git a/src/CSS/DOMTraverser/Util.php b/src/CSS/DOMTraverser/Util.php
index 033b14a..a1d7f3b 100644
--- a/src/CSS/DOMTraverser/Util.php
+++ b/src/CSS/DOMTraverser/Util.php
@@ -56,6 +56,8 @@ class Util
 	private const SELECTOR_ARGUMENT_PSEUDO_CLASSES = [
 		'not',
 		'matches',
+		'is',
+		'where',
 	];
 
 	/**
@@ -86,7 +88,7 @@ public static function isPositionalPseudoClass($name): bool
 	 * Check whether a pseudo-class has to be applied to the whole result set.
 	 *
 	 * That is true of the positional pseudo-classes themselves, and of
-	 * :not()/:matches() when their argument contains one.
+	 * :not()/:matches()/:is()/:where() when their argument contains one.
 	 *
 	 * @param string $name
 	 * @param mixed  $value
diff --git a/tests/Issues/Issue136Test.php b/tests/Issues/Issue136Test.php
new file mode 100644
index 0000000..81cc279
--- /dev/null
+++ b/tests/Issues/Issue136Test.php
@@ -0,0 +1,48 @@
+<?php
+/**
+ * @file
+ *
+ * Regression tests for https://github.com/GravityPDF/querypath/issues/136
+ *
+ * `:is()` and `:where()` are the CSS Selectors 4 names for `:matches()`. QueryPath does not use
+ * specificity, so `:where()` matches as `:is()` does.
+ */
+
+namespace QueryPathTests;
+
+class Issue136Test extends TestCase
+{
+	public const XML = '<?xml version="1.0"?><ul><li id="a"/><li id="b" class="x"/><li id="c" class="x"/></ul>';
+
+	/**
+	 * @dataProvider aliases
+	 */
+	public function testAliasesMatchAsMatchesDoes(string $name)
+	{
+		$this->assertSame('b', $this->idList(qp(self::XML)->find("li:$name(#b)")));
+		$this->assertSame('b', $this->idList(qp(self::XML)->find(":$name(#b)")));
+		$this->assertSame('a,b', $this->idList(qp(self::XML)->find("li:$name(#a, #b)")));
+		$this->assertSame('a', $this->idList(qp(self::XML)->find("li:not(:$name(.x))")));
+		$this->assertSame('b,c', $this->idList(qp(self::XML, 'li')->filter(":$name(.x)")));
+		$this->assertTrue(qp(self::XML, '#c')->is(":$name(.x)"));
+	}
+
+	/**
+	 * @dataProvider aliases
+	 */
+	public function testPositionalArgumentIsAppliedToTheSet(string $name)
+	{
+		$this->assertSame('a', $this->idList(qp(self::XML)->find("li:$name(:first)")));
+		$this->assertSame('b', $this->idList(qp(self::XML)->find("li:$name(.x:first)")));
+		$this->assertSame('a,c', $this->idList(qp(self::XML)->find("li:not(:$name(:eq(1)))")));
+	}
+
+	public function aliases(): array
+	{
+		return [
+			'is'         => ['is'],
+			'where'      => ['where'],
+			'upper case' => ['IS'],
+		];
+	}
+}