diff --git a/src/core/calculate.js b/src/core/calculate.js
index f05b1ae..70510e5 100644
--- a/src/core/calculate.js
+++ b/src/core/calculate.js
@@ -161,6 +161,18 @@ const calculateForAST = (selectorAST) => {
                         c += 1;
                         break;
 
+                    case 'highlight':
+                        if (child.children?.size > 0) {
+                            // The specificity of a ::highlight() selector with a * argument is zero.
+                            if (child.children.first?.value === '*') {
+                                break;
+                            }
+                            // The specificity of a ::highlight() selector with a <custom-ident> argument
+                            // is equivalent to a type selector.
+                            c += 1;
+                        }
+                        break;
+
                     default:
                         c += 1;
                         break;
diff --git a/test/index.js b/test/index.js
index 6d32d1f..57ec6bb 100644
--- a/test/index.js
+++ b/test/index.js
@@ -77,6 +77,24 @@ describe('CALCULATE', () => {
         it('::first-letter', () => {
             deepEqual(Specificity.calculate('::first-letter')[0].toObject(), { a: 0, b: 0, c: 1 });
         });
+        it('::part(my-ident)', () => {
+            deepEqual(Specificity.calculate('::part(my-ident)')[0].toObject(), { a: 0, b: 0, c: 1 });
+        });
+        it('::part(first-ident second-ident)', () => {
+            deepEqual(Specificity.calculate('::part(first-ident second-ident)')[0].toObject(), { a: 0, b: 0, c: 1 });
+        });
+        it('::highlight & do not crash', () => {
+            deepEqual(Specificity.calculate('::highlight')[0].toObject(), { a: 0, b: 0, c: 0 });
+        });
+        it('::highlight() & do not crash', () => {
+            deepEqual(Specificity.calculate('::highlight')[0].toObject(), { a: 0, b: 0, c: 0 });
+        });
+        it('::highlight(my-ident)', () => {
+            deepEqual(Specificity.calculate('::highlight(my-ident)')[0].toObject(), { a: 0, b: 0, c: 1 });
+        });
+        it('::highlight(*)', () => {
+            deepEqual(Specificity.calculate('::highlight(*)')[0].toObject(), { a: 0, b: 0, c: 0 });
+        });
     });
 
     describe('Pseudo-Element Selector ::slotted', () => {