diff --git a/packages/language-server/src/html-regions.ts b/packages/language-server/src/html-regions.ts
index 076f8c91..5fb9bd9a 100644
--- a/packages/language-server/src/html-regions.ts
+++ b/packages/language-server/src/html-regions.ts
@@ -100,12 +100,16 @@ export function isInsideHtml(document: TextDocument, offset: number): boolean {
 const regionCache = new Map<string, { version: number; regions: HtmlRegion[] }>();
 
 function regionsFor(document: TextDocument): HtmlRegion[] {
-  const version = document.version ?? -1;
+  // Documents without a version have no way to signal changes, so bypass cache.
+  if (document.version === undefined) {
+    return viewRegions(document.text);
+  }
+
   const cached = regionCache.get(document.uri);
-  if (cached && cached.version === version) return cached.regions;
+  if (cached && cached.version === document.version) return cached.regions;
 
   const regions = viewRegions(document.text);
-  regionCache.set(document.uri, { version, regions });
+  regionCache.set(document.uri, { version: document.version, regions });
   return regions;
 }
 
diff --git a/packages/language-server/test/html-regions.test.ts b/packages/language-server/test/html-regions.test.ts
index bf13dd24..78d19be4 100644
--- a/packages/language-server/test/html-regions.test.ts
+++ b/packages/language-server/test/html-regions.test.ts
@@ -107,3 +107,19 @@ test("isInsideHtml distinguishes markup from surrounding code", () => {
   expect(isInsideHtml(source, markupOffset)).toBe(true);
   expect(isInsideHtml(source, keywordOffset)).toBe(false);
 });
+
+test("documents without a version field scan every time and detect mutations", () => {
+  // Without a version, the cache has no key to validate freshness. Mutations
+  // must be detected on every call, even when uri and document are reused.
+  const source = doc(PAGE);
+  // Explicitly verify version is undefined (not set by doc() helper).
+  expect(source.version).toBeUndefined();
+
+  const markupOffset = PAGE.indexOf("<div");
+  expect(isInsideHtml(source, markupOffset)).toBe(true);
+
+  // Mutate the text: remove the view block.
+  source.text = "page A { }";
+  // Same uri, same missing version, but different text: mutation must be detected.
+  expect(isInsideHtml(source, markupOffset)).toBe(false);
+});