diff --git a/extensions/memory-wiki/src/markdown.test.ts b/extensions/memory-wiki/src/markdown.test.ts
index d78a5c0d803..8315fdda5b8 100644
--- a/extensions/memory-wiki/src/markdown.test.ts
+++ b/extensions/memory-wiki/src/markdown.test.ts
@@ -41,7 +41,7 @@ describe("slugifyWikiSegment", () => {
     const fileName = createWikiPageFilename(stem);
 
     expect(fileName.endsWith(".md")).toBe(true);
-    expect(Buffer.byteLength(fileName)).toBeLessThanOrEqual(255);
+    expect(Buffer.byteLength(`.${fileName}.fallback.tmp`)).toBeLessThanOrEqual(255);
     expect(createWikiPageFilename(stem)).toBe(fileName);
   });
 });
diff --git a/extensions/memory-wiki/src/markdown.ts b/extensions/memory-wiki/src/markdown.ts
index 31d7ca95579..9137642095a 100644
--- a/extensions/memory-wiki/src/markdown.ts
+++ b/extensions/memory-wiki/src/markdown.ts
@@ -109,6 +109,8 @@ const RELATED_BLOCK_PATTERN = new RegExp(
 );
 const MAX_WIKI_SEGMENT_BYTES = 240;
 const MAX_WIKI_FILENAME_COMPONENT_BYTES = 255;
+const MAX_WIKI_SAFE_WRITE_FILENAME_COMPONENT_BYTES =
+  MAX_WIKI_FILENAME_COMPONENT_BYTES - Buffer.byteLength(".fallback.tmp") - 1;
 const WIKI_SEGMENT_HASH_BYTES = 12;
 
 function truncateUtf8CodePointSafe(value: string, maxBytes: number): string {
@@ -152,7 +154,7 @@ export function createWikiPageFilename(stem: string, extension = ".md"): string
   const normalizedExtension = extension.startsWith(".") ? extension : `.${extension}`;
   const maxStemBytes = Math.max(
     1,
-    MAX_WIKI_FILENAME_COMPONENT_BYTES - Buffer.byteLength(normalizedExtension),
+    MAX_WIKI_SAFE_WRITE_FILENAME_COMPONENT_BYTES - Buffer.byteLength(normalizedExtension),
   );
   return `${capWikiValueWithHash(stem, maxStemBytes, "page")}${normalizedExtension}`;
 }