diff --git a/components/selectors/parser.rs b/components/selectors/parser.rs
index 601b7e23986..9f33683b950 100644
--- a/components/selectors/parser.rs
+++ b/components/selectors/parser.rs
@@ -1021,6 +1021,7 @@ impl<Impl: SelectorImpl> ToCss for Component<Impl> {
                 (0, 0) => dest.write_char('0'),
 
                 (1, 0) => dest.write_char('n'),
+                (-1, 0) => dest.write_str("-n"),
                 (_, 0) => write!(dest, "{}n", a),
 
                 (0, _) => write!(dest, "{}", b),
diff --git a/tests/wpt/metadata/css/selectors/anplusb-selector-parsing.html.ini b/tests/wpt/metadata/css/selectors/anplusb-selector-parsing.html.ini
deleted file mode 100644
index d7923415b01..00000000000
--- a/tests/wpt/metadata/css/selectors/anplusb-selector-parsing.html.ini
+++ /dev/null
@@ -1,25 +0,0 @@
-[anplusb-selector-parsing.html]
-  [:nth-child(-n+0) should be parsed and serialized correctly]
-    expected: FAIL
-
-  [:nth-child(-n) should be parsed and serialized correctly]
-    expected: FAIL
-
-  [:nth-last-child(-n+0) should be parsed and serialized correctly]
-    expected: FAIL
-
-  [:nth-last-child(-n) should be parsed and serialized correctly]
-    expected: FAIL
-
-  [:nth-of-type(-n+0) should be parsed and serialized correctly]
-    expected: FAIL
-
-  [:nth-of-type(-n) should be parsed and serialized correctly]
-    expected: FAIL
-
-  [:nth-last-of-type(-n+0) should be parsed and serialized correctly]
-    expected: FAIL
-
-  [:nth-last-of-type(-n) should be parsed and serialized correctly]
-    expected: FAIL
-