diff --git a/src/browser/tests/css/external_stylesheet.html b/src/browser/tests/css/external_stylesheet.html
index 10b38042..a98520ad 100644
--- a/src/browser/tests/css/external_stylesheet.html
+++ b/src/browser/tests/css/external_stylesheet.html
@@ -125,22 +125,28 @@
   {
     // Stylesheet links parsed via innerHTML / outerHTML /
     // insertAdjacentHTML / Range.createContextualFragment / <template>
-    // content must NOT trigger a network fetch or register a sheet on
-    // the live document — the owning subtree may never be attached.
-    // Regression test for the fragment-mode bypass caught in code review.
+    // content / DOMParser.parseFromString must NOT trigger a network
+    // fetch or register a sheet on the live document — the owning
+    // subtree may never be attached or belongs to a different Document.
     //
-    // Assertion is synchronous on purpose: parseHtmlAsChildren runs
-    // inline, so any unintended sheet registration would be visible
-    // immediately. Deferring to testing.onload would race against the
-    // async tests above that legitimately add sheets.
-    //
-    // DOMParser.parseFromString is a separate case (parses with
-    // `_parse_mode = .document` into a *different* Document) and is not
-    // covered by the same gate — tracked as a follow-up.
+    // Assertion is synchronous on purpose: both parse paths run inline,
+    // so any unintended sheet registration would be visible immediately.
+    // Deferring to testing.onload would race against the async tests
+    // above that legitimately add sheets.
     const before = document.styleSheets.length;
+
     const div = document.createElement('div');
     div.innerHTML = '<link rel="stylesheet" href="/styles/visibility.css">';
     testing.expectEqual(before, document.styleSheets.length);
+
+    const parsed = new DOMParser().parseFromString(
+      '<html><head><link rel="stylesheet" href="/styles/visibility2.css"></head><body></body></html>',
+      'text/html'
+    );
+    // Parsed link exists in the new document...
+    testing.expectEqual(1, parsed.querySelectorAll('link').length);
+    // ...but no sheet on the live document.
+    testing.expectEqual(before, document.styleSheets.length);
   }
   </script>
 
diff --git a/src/browser/webapi/DOMParser.zig b/src/browser/webapi/DOMParser.zig
index f06027c5..d0356803 100644
--- a/src/browser/webapi/DOMParser.zig
+++ b/src/browser/webapi/DOMParser.zig
@@ -53,6 +53,17 @@ pub fn parseFromString(
     const arena = try frame.getArena(.medium, "DOMParser.parseFromString");
     defer frame.releaseArena(arena);
 
+    // DOMParser builds a detached Document. Borrow the same fragment
+    // parse-mode that `parseHtmlAsChildren` uses so frame-side hooks
+    // triggered from `Build.created` / `nodeIsReady` (external stylesheet
+    // fetches, script execution, mutation-observer fan-out, default-script
+    // injection) treat the parsed nodes as detached and skip
+    // side effects on the live document. The frame's `_parse_mode` is
+    // restored on exit.
+    const previous_parse_mode = frame._parse_mode;
+    frame._parse_mode = .fragment;
+    defer frame._parse_mode = previous_parse_mode;
+
     return switch (target_mime) {
         .@"text/html" => {
             // Create a new HTMLDocument
