--- a/dom/media/gtest/moz.build
+++ b/dom/media/gtest/moz.build
@@ -26,16 +26,17 @@ UNIFIED_SOURCES += [
     'TestVideoSegment.cpp',
     'TestVideoUtils.cpp',
     'TestVPXDecoding.cpp',
     'TestWebMBuffered.cpp',
 ]
 
 if CONFIG['MOZ_WEBM_ENCODER']:
     UNIFIED_SOURCES += [
+        'TestAudioTrackEncoder.cpp',
         'TestVideoTrackEncoder.cpp',
         'TestWebMWriter.cpp',
     ]
 
 TEST_HARNESS_FILES.gtest += [
     '../test/gizmo-frag.mp4',
     '../test/gizmo.mp4',
     '../test/vp9cake.webm',