diff --git a/src/build-source-map-tree.ts b/src/build-source-map-tree.ts
index f12cf52..ffd0ba0 100644
--- a/src/build-source-map-tree.ts
+++ b/src/build-source-map-tree.ts
@@ -31,7 +31,7 @@ export default function buildSourceMapTree(
   const map = maps.pop()!;
 
   for (let i = 0; i < maps.length; i++) {
-    if (maps[i].sources.length !== 1) {
+    if (maps[i].sources.length > 1) {
       throw new Error(
         `Transformation map ${i} must have exactly one source file.\n` +
           'Did you specify these with the most recent transformation maps first?'
diff --git a/test/samples/sourceless-transform/test.ts b/test/samples/sourceless-transform/test.ts
new file mode 100644
index 0000000..9318bb7
--- /dev/null
+++ b/test/samples/sourceless-transform/test.ts
@@ -0,0 +1,37 @@
+import remapping from '../../../src/remapping';
+
+describe('source-less transform', () => {
+  const original: any = {
+    version: '3',
+    sources: ['source.ts'],
+    names: [],
+    mappings: 'AAAA',
+    sourcesContent: ['// hello'],
+  };
+  const minified: any = {
+    version: '3',
+    sources: [],
+    names: [],
+    mappings: '',
+  };
+
+  test('remapping with loader generates empty sourcemap', () => {
+    const loader = jest.fn(() => null);
+    loader.mockReturnValueOnce(original);
+    const remapped = remapping(minified, loader);
+
+    expect(loader).not.toHaveBeenCalled();
+    expect(remapped.sources).toHaveLength(0);
+    expect(remapped.mappings).toBe('');
+  });
+
+  test('remapping with array shorthand generates empty sourcemap', () => {
+    const loader = jest.fn(() => null);
+    const remapped = remapping([minified, original], loader);
+
+    expect(loader).toHaveBeenCalledTimes(1);
+    expect(loader).toHaveBeenCalledWith('source.ts');
+    expect(remapped.sources).toHaveLength(0);
+    expect(remapped.mappings).toBe('');
+  });
+});