diff --git a/components/script/dom/htmlareaelement.rs b/components/script/dom/htmlareaelement.rs
index a342e0ab2dd..535d296a29f 100644
--- a/components/script/dom/htmlareaelement.rs
+++ b/components/script/dom/htmlareaelement.rs
@@ -207,6 +207,7 @@ impl Area {
 
             Area::Polygon { ref points } => {
                 // Ray-casting algorithm to determine if point is inside polygon
+                // https://en.wikipedia.org/wiki/Point_in_polygon#Ray_casting_algorithm
                 let mut inside = false;
 
                 debug_assert!(points.len() % 2 == 0);
diff --git a/tests/unit/script/htmlareaelement.rs b/tests/unit/script/htmlareaelement.rs
index faa33c25940..becfd17b88a 100644
--- a/tests/unit/script/htmlareaelement.rs
+++ b/tests/unit/script/htmlareaelement.rs
@@ -196,4 +196,10 @@ fn test_hit_test_polygon() {
     assert!(!poly3.hit_test(&Point2D::new(6.0, 0.0)));
     assert!(!poly3.hit_test(&Point2D::new(0.0, 6.0)));
     assert!(!poly3.hit_test(&Point2D::new(6.0, 6.0)));
+    // Concave polygon test
+    let poly4 = Area::Polygon {
+        points: vec![0.0, 0.0, 1.0, 1.0, 2.0, 0.0, 2.0, 2.0, 0.0, 2.0],
+    };
+    assert!(poly4.hit_test(&Point2D::new(1.5, 1.5)));
+    assert!(!poly4.hit_test(&Point2D::new(1.0, 0.0)));
 }