diff --git a/src/scan.js b/src/scan.js
index 4aaf77f..fa11ad2 100644
--- a/src/scan.js
+++ b/src/scan.js
@@ -96,11 +96,23 @@ function validateReview(review) {
   }
   return { errors };
 }
-// Scan backward from the last } to find its depth-matching { so that stray
-// brace pairs in prose before the JSON block (e.g. `Foo{}`) are skipped.
+// Return the JSON object that ends at the last }. Stray brace pairs in prose
+// before the JSON block (e.g. `Foo{}`) must be skipped, but counting braces
+// alone breaks on string values with unmatched braces (e.g. `impl Foo {`), so
+// take the earliest { whose slice parses. If none does, fall back to the
+// depth-matching { and let the caller report the parse error.
 function extractJson(text) {
   const lastBrace = text.lastIndexOf('}');
   if (lastBrace === -1) return null;
+  for (let i = text.indexOf('{'); i !== -1 && i < lastBrace; i = text.indexOf('{', i + 1)) {
+    const candidate = text.slice(i, lastBrace + 1);
+    try {
+      JSON.parse(candidate);
+      return candidate;
+    } catch {
+      // not the start of the JSON block
+    }
+  }
   let depth = 0;
   for (let i = lastBrace; i >= 0; i--) {
     if (text[i] === '}') depth++;
diff --git a/tests/scan.test.js b/tests/scan.test.js
index cd33aab..fc0fd83 100644
--- a/tests/scan.test.js
+++ b/tests/scan.test.js
@@ -301,3 +301,23 @@ test('extractJson - handles JSON with brace pairs inside string values', () => {
   const json = '{"body":"use {} syntax","event":"COMMENT","comments":[]}';
   assert.equal(extractJson(json), json);
 });
+
+test('extractJson - handles JSON with unmatched braces inside string values', () => {
+  for (const body of ['The block opened by `impl Foo {` is never closed.', 'Drop the extra `}`.']) {
+    const json = JSON.stringify({
+      body: 'Summary.',
+      event: 'COMMENT',
+      comments: [
+        { path: 'src/a.rs', line: 10, side: 'RIGHT', body },
+        { path: 'src/b.rs', line: 20, side: 'RIGHT', body: 'Second comment.' },
+      ],
+    }, null, 2);
+    assert.equal(extractJson(json), json);
+    assert.equal(extractJson('Here is the review: {not json}\n```json\n' + json + '\n```'), json);
+  }
+});
+
+test('extractJson - falls back to the depth-matching brace when nothing parses', () => {
+  const broken = '{"body":"ok","event":"COMMENT","comments":[{"path":"a"},]}';
+  assert.equal(extractJson('Some {prose}. ' + broken), broken);
+});