diff --git a/crates/svg/src/import/css.rs b/crates/svg/src/import/css.rs
index b5f1d80320..7bf440cc73 100644
--- a/crates/svg/src/import/css.rs
+++ b/crates/svg/src/import/css.rs
@@ -556,10 +556,12 @@ impl Styles {
     }
 
     /// The properties rules with a `:not()` set on `n`, each with its value after the cascade.
+    /// Only the rules [`Index::candidates`] gives for `n` are tested, as in [`Styles::matched_bytes`].
     pub(super) fn set_by_not_rules(&self, n: XNode) -> Vec<(String, String)> {
         let declared = self.declared(n);
         let mut out: Vec<(String, String)> = Vec::new();
-        for r in self.rules.iter().filter(|r| r.selector.has_not() && r.selector.matches(n)) {
+        let rules = self.index.candidates(n).into_iter().filter_map(|i| self.rules.get(i));
+        for r in rules.filter(|r| r.selector.has_not() && r.selector.matches(n)) {
             for (k, ..) in r.decls.iter() {
                 if !out.iter().any(|(o, _)| o == k)
                     && let Some(v) = declared.get(k)
diff --git a/crates/svg/src/import/css/tests.rs b/crates/svg/src/import/css/tests.rs
index 2e78c4da98..5c9e305c27 100644
--- a/crates/svg/src/import/css/tests.rs
+++ b/crates/svg/src/import/css/tests.rs
@@ -334,6 +334,26 @@ fn not_selectors() {
     );
 }
 
+/// The `:not()` rules filed under classes an element lacks are not tested against it, so
+/// [`Styles::set_by_not_rules`] tests no more rules than [`Styles::matched_bytes`] counts.
+#[test]
+fn not_rules_test_only_the_indexed_candidates() {
+    const N: usize = 2_000;
+    let rules: String = (0..N).map(|i| format!(".c{i}:not(.skip) {{ fill: #{i:06x} }}\n")).collect();
+    let rects: String = (0..N).map(|i| format!(r#"<rect id="r{i}" class="c{i}"/>"#)).collect();
+    let svg = format!(r#"<svg xmlns="http://www.w3.org/2000/svg"><style>{rules}</style>{rects}<rect id="skip" class="c0 skip"/></svg>"#);
+    with_doc(&svg, |doc, st| {
+        let before = selector_tests();
+        for i in 0..N {
+            assert_eq!(st.set_by_not_rules(by_id(doc, &format!("r{i}"))), [("fill".to_string(), format!("#{i:06x}"))]);
+        }
+        assert!(st.set_by_not_rules(by_id(doc, "skip")).is_empty());
+        // Testing every `:not()` rule against every element would test N × N selectors.
+        let tests = selector_tests() - before;
+        assert!(tests <= 3 * N as u64, "finding the :not() rules of {N} elements tested {tests} selectors");
+    });
+}
+
 #[test]
 fn decl_comments_are_stripped() {
     let d = |k: &str, v: &str| (k.to_string(), v.to_string(), false);