diff --git a/dom/media/webm/moz.build b/dom/media/webm/moz.build
index f2898fafd4..4dacfe0953 100644
--- a/dom/media/webm/moz.build
+++ b/dom/media/webm/moz.build
@@ -11,7 +11,7 @@ EXPORTS += [
     'WebMDemuxer.h',
 ]
 
-UNIFIED_SOURCES += [
+SOURCES += [
     'WebMBufferedParser.cpp',
     'WebMDecoder.cpp',
     'WebMDemuxer.cpp',
@@ -19,8 +19,10 @@ UNIFIED_SOURCES += [
 
 if CONFIG['MOZ_WEBM_ENCODER']:
     EXPORTS += ['WebMWriter.h']
-    UNIFIED_SOURCES += ['EbmlComposer.cpp',
-                        'WebMWriter.cpp',
+
+    SOURCES += [
+        'EbmlComposer.cpp',
+        'WebMWriter.cpp',
     ]
 
 CXXFLAGS += CONFIG['MOZ_LIBVPX_CFLAGS']