diff --git a/scripts/cross-post-devto.mts b/scripts/cross-post-devto.mts
index e4b3d8f..5396b0a 100644
--- a/scripts/cross-post-devto.mts
+++ b/scripts/cross-post-devto.mts
@@ -480,11 +480,24 @@ function loadFromFile(filePath: string): ArticleInput {
 
   const raw = readFileSync(absPath, "utf-8");
   const { frontmatter, body } = parseFrontmatter(raw);
-  const slug = basename(absPath, ".md");
+  const slug = deriveSlug(absPath);
 
   return { slug, frontmatter, body };
 }
 
+// Derive a manifest key from the file path. When the markdown file follows the
+// convention {article-slug}/devto.md, basename() alone gives "devto", which
+// collides across articles and causes silent overwrites in --update mode.
+// Fall back to the parent directory name for generic filenames; otherwise use
+// the filename as before (backwards-compatible for standalone .md files).
+function deriveSlug(absPath: string): string {
+  const base = basename(absPath, ".md");
+  if (base === "devto" || base === "qiita") {
+    return basename(dirname(absPath));
+  }
+  return base;
+}
+
 function loadFromDir(dirPath: string): ArticleInput[] {
   const absDir = resolve(dirPath);
   if (!existsSync(absDir)) {
diff --git a/scripts/cross-post-qiita.mts b/scripts/cross-post-qiita.mts
index 3776aa1..9323ad5 100644
--- a/scripts/cross-post-qiita.mts
+++ b/scripts/cross-post-qiita.mts
@@ -295,11 +295,24 @@ function loadFromFile(filePath: string): ArticleInput {
 
   const raw = readFileSync(absPath, "utf-8");
   const { frontmatter, body } = parseFrontmatter(raw);
-  const slug = basename(absPath, ".md");
+  const slug = deriveSlug(absPath);
 
   return { slug, frontmatter, body };
 }
 
+// Derive a manifest key from the file path. When the markdown file follows the
+// convention {article-slug}/qiita.md, basename() alone gives "qiita", which
+// collides across articles and causes silent overwrites in --update mode.
+// Fall back to the parent directory name for generic filenames; otherwise use
+// the filename as before (backwards-compatible for standalone .md files).
+function deriveSlug(absPath: string): string {
+  const base = basename(absPath, ".md");
+  if (base === "devto" || base === "qiita") {
+    return basename(dirname(absPath));
+  }
+  return base;
+}
+
 function loadFromDir(dirPath: string): ArticleInput[] {
   const absDir = resolve(dirPath);
   if (!existsSync(absDir)) {