diff --git a/components/style/rule_tree/mod.rs b/components/style/rule_tree/mod.rs
index 22a862cac5f..2557b4c77e5 100644
--- a/components/style/rule_tree/mod.rs
+++ b/components/style/rule_tree/mod.rs
@@ -61,6 +61,12 @@ pub enum StyleSource {
     Declarations(Arc<Locked<PropertyDeclarationBlock>>),
 }
 
+impl PartialEq for StyleSource {
+    fn eq(&self, other: &Self) -> bool {
+        self.ptr_equals(other)
+    }
+}
+
 impl StyleSource {
     #[inline]
     fn ptr_equals(&self, other: &Self) -> bool {