diff --git a/testing/web-platform/tests/url/resources/setters_tests.json b/testing/web-platform/tests/url/resources/setters_tests.json
index 56bcae464a6f5..69c36d01536bd 100644
--- a/testing/web-platform/tests/url/resources/setters_tests.json
+++ b/testing/web-platform/tests/url/resources/setters_tests.json
@@ -990,6 +990,26 @@
                 "hostname": "test",
                 "port": "12"
             }
+        },
+        {
+            "comment": "Leading / is not stripped",
+            "href": "http://example.com/",
+            "new_value": "///bad.com",
+            "expected": {
+                "href": "http://example.com/",
+                "host": "example.com",
+                "hostname": "example.com"
+            }
+        },
+        {
+            "comment": "Leading / is not stripped",
+            "href": "sc://example.com/",
+            "new_value": "///bad.com",
+            "expected": {
+                "href": "sc:///",
+                "host": "",
+                "hostname": ""
+            }
         }
     ],
     "hostname": [
@@ -1345,6 +1365,26 @@
                 "hostname": "",
                 "pathname": "//p"
             }
+        },
+        {
+            "comment": "Leading / is not stripped",
+            "href": "http://example.com/",
+            "new_value": "///bad.com",
+            "expected": {
+                "href": "http://example.com/",
+                "host": "example.com",
+                "hostname": "example.com"
+            }
+        },
+        {
+            "comment": "Leading / is not stripped",
+            "href": "sc://example.com/",
+            "new_value": "///bad.com",
+            "expected": {
+                "href": "sc:///",
+                "host": "",
+                "hostname": ""
+            }
         }
     ],
     "port": [
@@ -1667,6 +1707,24 @@
                 "pathname": "/%23"
             }
         },
+        {
+            "comment": "? doesn't mess up encoding",
+            "href": "http://example.net",
+            "new_value": "/?é",
+            "expected": {
+                "href": "http://example.net/%3F%C3%A9",
+                "pathname": "/%3F%C3%A9"
+            }
+        },
+        {
+            "comment": "# doesn't mess up encoding",
+            "href": "http://example.net",
+            "new_value": "/#é",
+            "expected": {
+                "href": "http://example.net/%23%C3%A9",
+                "pathname": "/%23%C3%A9"
+            }
+        },
         {
             "comment": "File URLs and (back)slashes",
             "href": "file://monkey/",
diff --git a/testing/web-platform/tests/url/resources/urltestdata.json b/testing/web-platform/tests/url/resources/urltestdata.json
index 96c42d2284ebf..d20e8482c193d 100644
--- a/testing/web-platform/tests/url/resources/urltestdata.json
+++ b/testing/web-platform/tests/url/resources/urltestdata.json
@@ -539,6 +539,36 @@
     "search": "",
     "hash": ""
   },
+  {
+    "input": "\\x",
+    "base": "http://example.org/foo/bar",
+    "href": "http://example.org/x",
+    "origin": "http://example.org",
+    "protocol": "http:",
+    "username": "",
+    "password": "",
+    "host": "example.org",
+    "hostname": "example.org",
+    "port": "",
+    "pathname": "/x",
+    "search": "",
+    "hash": ""
+  },
+  {
+    "input": "\\\\x\\hello",
+    "base": "http://example.org/foo/bar",
+    "href": "http://x/hello",
+    "origin": "http://x",
+    "protocol": "http:",
+    "username": "",
+    "password": "",
+    "host": "x",
+    "hostname": "x",
+    "port": "",
+    "pathname": "/hello",
+    "search": "",
+    "hash": ""
+  },
   {
     "input": "::",
     "base": "http://example.org/foo/bar",