diff --git a/packages/schematics/angular/migrations/use-library-builder/migration.ts b/packages/schematics/angular/migrations/use-library-builder/migration.ts
index 68f9e8738e25..285cdf9f2332 100644
--- a/packages/schematics/angular/migrations/use-library-builder/migration.ts
+++ b/packages/schematics/angular/migrations/use-library-builder/migration.ts
@@ -251,7 +251,23 @@ function migrateTargetOptions(
       : [];
     const migratedAssets = ngPackageConfig.assets.map((asset) => {
       if (typeof asset === 'string') {
-        return join(projectDir, asset);
+        const assetPath = join(projectDir, asset);
+        if (assetPath.startsWith('..')) {
+          return assetPath;
+        }
+
+        if (tree.exists(assetPath)) {
+          return assetPath;
+        }
+
+        const assetDir = tree.getDir(assetPath);
+        if (assetDir.subfiles.length || assetDir.subdirs.length) {
+          return assetPath;
+        }
+
+        // `ng-packagr` treats a string that is neither a file nor a directory as a glob relative
+        // to the package root, while the library builder only accepts files and directories.
+        return { glob: asset, input: projectDir };
       }
       if (isJsonObject(asset) && typeof asset['input'] === 'string') {
         return {
diff --git a/packages/schematics/angular/migrations/use-library-builder/migration_spec.ts b/packages/schematics/angular/migrations/use-library-builder/migration_spec.ts
index 11192f8e5897..d54d5f62f61a 100644
--- a/packages/schematics/angular/migrations/use-library-builder/migration_spec.ts
+++ b/packages/schematics/angular/migrations/use-library-builder/migration_spec.ts
@@ -281,6 +281,7 @@ describe('Migration to use the library builder', () => {
   });
 
   it('should migrate assets, styleIncludePaths, and sass options from ng-package.json', async () => {
+    tree.create('/projects/my-lib/CHANGELOG.md', '# Changelog');
     tree.overwrite(
       '/projects/my-lib/ng-package.json',
       JSON.stringify(
@@ -324,6 +325,48 @@ describe('Migration to use the library builder', () => {
     });
   });
 
+  it('should migrate ng-packagr glob string assets to glob objects', async () => {
+    tree.create('/projects/my-lib/docs/guide.md', '# Guide');
+    tree.create('/projects/my-lib/CHANGELOG.md', '# Changelog');
+    tree.overwrite(
+      '/projects/my-lib/ng-package.json',
+      JSON.stringify({
+        assets: ['CHANGELOG.md', 'docs', 'docs/**/*.md'],
+        lib: { entryFile: 'src/public-api.ts' },
+      }),
+    );
+
+    const newTree = await schematicRunner.runSchematic(schematicName, {}, tree);
+    const {
+      projects: { 'my-lib': lib },
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    } = newTree.readJson('/angular.json') as any;
+
+    expect(lib.architect['build'].options.assets).toEqual([
+      'projects/my-lib/CHANGELOG.md',
+      'projects/my-lib/docs',
+      { glob: 'docs/**/*.md', input: 'projects/my-lib' },
+    ]);
+  });
+
+  it('should keep ng-packagr assets outside the project root as paths', async () => {
+    tree.overwrite(
+      '/projects/my-lib/ng-package.json',
+      JSON.stringify({
+        assets: ['../../../shared-assets'],
+        lib: { entryFile: 'src/public-api.ts' },
+      }),
+    );
+
+    const newTree = await schematicRunner.runSchematic(schematicName, {}, tree);
+    const {
+      projects: { 'my-lib': lib },
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    } = newTree.readJson('/angular.json') as any;
+
+    expect(lib.architect['build'].options.assets).toEqual(['../shared-assets']);
+  });
+
   it('should preserve existing stylePreprocessorOptions.includePaths when migrating styleIncludePaths', async () => {
     const angularJson = JSON.parse(tree.readContent('/angular.json'));
     angularJson.projects['my-lib'].architect.build.options.stylePreprocessorOptions = {