diff --git a/apps/readest-app/src/__tests__/services/dictionaries/groupBundlesByStem.test.ts b/apps/readest-app/src/__tests__/services/dictionaries/groupBundlesByStem.test.ts
new file mode 100644
index 00000000..6e69abff
--- /dev/null
+++ b/apps/readest-app/src/__tests__/services/dictionaries/groupBundlesByStem.test.ts
@@ -0,0 +1,90 @@
+/**
+ * groupBundlesByStem — MDict companion-MDD attachment.
+ *
+ * A single MDX often ships its resources across several MDD files named with a
+ * shared prefix (`Name.mdd`, `Name-01.mdd`, `Name.1.mdd`, …) — images in one,
+ * scripts in another, audio in a third. The importer must attach every MDD
+ * whose stem starts with the MDX stem (at a separator boundary) to that MDX
+ * bundle; `.css` is pooled by name-independent rule (unchanged).
+ */
+import { describe, it, expect } from 'vitest';
+import { groupBundlesByStem } from '@/services/dictionaries/dictionaryService';
+import type { SelectedFile } from '@/hooks/useFileSelector';
+
+const sf = (name: string): SelectedFile => ({ path: `/books/${name}` });
+
+const mdictBundle = (files: string[]) => {
+  const { bundles, orphans } = groupBundlesByStem(files.map(sf));
+  const mdict = bundles.find((b) => b.kind === 'mdict');
+  return {
+    mdx: mdict && mdict.kind === 'mdict' ? mdict.mdx.name : null,
+    mdds: mdict && mdict.kind === 'mdict' ? mdict.mdd.map((m) => m.name).sort() : [],
+    css: mdict && mdict.kind === 'mdict' ? mdict.css.map((c) => c.name).sort() : [],
+    bundleCount: bundles.filter((b) => b.kind === 'mdict').length,
+    orphans: orphans.map((o) => o.name).sort(),
+  };
+};
+
+describe('groupBundlesByStem — MDict companion MDDs', () => {
+  it('attaches dash-numbered companion MDDs (vocabulary.com layout)', () => {
+    const r = mdictBundle([
+      'Vocabulary.com Dictionary.mdx',
+      'Vocabulary.com Dictionary.mdd',
+      'Vocabulary.com Dictionary-01.mdd',
+      'Vocabulary.com Dictionary-02.mdd',
+      'Vocabulary.com Dictionary-03.mdd',
+    ]);
+    expect(r.mdx).toBe('Vocabulary.com Dictionary.mdx');
+    expect(r.mdds).toEqual([
+      'Vocabulary.com Dictionary-01.mdd',
+      'Vocabulary.com Dictionary-02.mdd',
+      'Vocabulary.com Dictionary-03.mdd',
+      'Vocabulary.com Dictionary.mdd',
+    ]);
+    expect(r.orphans).toEqual([]);
+  });
+
+  it('attaches dot-numbered companion MDDs (.1/.2 convention)', () => {
+    const r = mdictBundle(['Base.mdx', 'Base.mdd', 'Base.1.mdd', 'Base.2.mdd']);
+    expect(r.mdds).toEqual(['Base.1.mdd', 'Base.2.mdd', 'Base.mdd']);
+    expect(r.orphans).toEqual([]);
+  });
+
+  it('still attaches the single exact-stem MDD (existing behavior)', () => {
+    const r = mdictBundle(['Base.mdx', 'Base.mdd']);
+    expect(r.mdds).toEqual(['Base.mdd']);
+    expect(r.orphans).toEqual([]);
+  });
+
+  it('does not merge an unrelated MDD that only shares a word prefix', () => {
+    // `dict` is a prefix of `dictionary-words` as a string, but the next char
+    // ('i') is not a separator, so it must NOT attach.
+    const r = mdictBundle(['dict.mdx', 'dict.mdd', 'dictionary-words.mdd']);
+    expect(r.mdds).toEqual(['dict.mdd']);
+    expect(r.orphans).toEqual(['dictionary-words.mdd']);
+  });
+
+  it('attaches a companion MDD to the longest matching MDX prefix', () => {
+    const { bundles } = groupBundlesByStem(
+      ['dict.mdx', 'dictionary.mdx', 'dictionary-01.mdd'].map(sf),
+    );
+    const dictionary = bundles.find((b) => b.kind === 'mdict' && b.mdx.name === 'dictionary.mdx');
+    const dict = bundles.find((b) => b.kind === 'mdict' && b.mdx.name === 'dict.mdx');
+    expect(
+      dictionary && dictionary.kind === 'mdict' ? dictionary.mdd.map((m) => m.name) : null,
+    ).toEqual(['dictionary-01.mdd']);
+    expect(dict && dict.kind === 'mdict' ? dict.mdd.map((m) => m.name) : null).toEqual([]);
+  });
+
+  it('pools .css of any name onto the MDict bundle (unchanged)', () => {
+    const r = mdictBundle(['Base.mdx', 'Base-01.mdd', 'arbitrary-name.css']);
+    expect(r.mdds).toEqual(['Base-01.mdd']);
+    expect(r.css).toEqual(['arbitrary-name.css']);
+  });
+
+  it('orphans companion MDDs when no MDX is present', () => {
+    const r = mdictBundle(['Base-01.mdd', 'Base-02.mdd']);
+    expect(r.bundleCount).toBe(0);
+    expect(r.orphans).toEqual(['Base-01.mdd', 'Base-02.mdd']);
+  });
+});
diff --git a/apps/readest-app/src/services/dictionaries/dictionaryService.ts b/apps/readest-app/src/services/dictionaries/dictionaryService.ts
index 2c7d470e..ad9a3224 100644
--- a/apps/readest-app/src/services/dictionaries/dictionaryService.ts
+++ b/apps/readest-app/src/services/dictionaries/dictionaryService.ts
@@ -113,6 +113,21 @@ function classify(source: SelectedFile): SourceFile {
   return { name, stem, ext, isDictZip, source };
 }
 
+/**
+ * True when `mddStem` is a numbered companion of the MDict bundle keyed by
+ * `bundleStem` — i.e. `bundleStem` followed by a separator (`Name-01`,
+ * `Name.1`, `Name 2`, …). A non-alphanumeric boundary is required so a
+ * different word can't match (`dict` must not claim `dictionary-words`). The
+ * exact-stem `Name.mdd` is already attached by the stem pass, so an exact
+ * match returns false here.
+ */
+function isCompanionMddStem(bundleStem: string, mddStem: string): boolean {
+  if (mddStem === bundleStem) return false;
+  if (!mddStem.startsWith(bundleStem)) return false;
+  const boundary = mddStem.charAt(bundleStem.length);
+  return boundary !== '' && !/[a-z0-9]/i.test(boundary);
+}
+
 /**
  * Group a flat list of selected files into StarDict and MDict bundles by
  * stem. Files that don't belong to any complete bundle land in `orphans`.
@@ -120,7 +135,9 @@ function classify(source: SelectedFile): SourceFile {
  * Rules:
  *  - StarDict bundle = exactly one `.ifo` + one `.idx` + one `.dict` or
  *    `.dict.dz` (sharing a stem). `.syn` is optional.
- *  - MDict bundle = one `.mdx` + zero or more `.mdd` (sharing a stem).
+ *  - MDict bundle = one `.mdx` + zero or more `.mdd` whose stem starts with the
+ *    `.mdx` stem at a separator boundary (`Name.mdd`, `Name-01.mdd`,
+ *    `Name.1.mdd`); each `.mdd` attaches to the longest matching `.mdx`.
  *  - DICT (dictd) bundle = one `.index` + one `.dict` or `.dict.dz`
  *    (sharing a stem). Note: `.idx` (StarDict) and `.index` (DICT) differ
  *    only by spelling — the StarDict branch wins when both are present.
@@ -166,6 +183,26 @@ export function groupBundlesByStem(files: SelectedFile[]): GroupResult {
     }
   }
 
+  // Attach numbered companion MDDs. A single MDX often splits its resources
+  // across several MDD files sharing its filename prefix (e.g. images in one,
+  // scripts in another, audio in a third); the stem pass above only catches the
+  // exact-stem `Name.mdd`. Rescue the rest from `orphans`, attaching each to the
+  // MDict bundle whose stem is the longest matching prefix.
+  const mdictForMdd = bundles
+    .filter((b): b is MDictGroup => b.kind === 'mdict')
+    .sort((a, b) => b.stem.length - a.stem.length);
+  if (mdictForMdd.length > 0) {
+    const stillOrphaned: SourceFile[] = [];
+    for (const f of orphans) {
+      const target =
+        f.ext === 'mdd' ? mdictForMdd.find((b) => isCompanionMddStem(b.stem, f.stem)) : undefined;
+      if (target) target.mdd.push(f);
+      else stillOrphaned.push(f);
+    }
+    orphans.length = 0;
+    orphans.push(...stillOrphaned);
+  }
+
   // Distribute all loose `.css` files across the MDict bundles in this
   // import. With one dictionary at a time (the common case) every selected
   // `.css` ends up applied; with multiple, each gets the full set — benign