diff --git a/aegisub/Makefile.am b/aegisub/Makefile.am
index 076cc92f8..62348ebe0 100644
--- a/aegisub/Makefile.am
+++ b/aegisub/Makefile.am
@@ -196,6 +196,7 @@ aegisub_SOURCES = \
 	audio_player.cpp \
 	audio_provider.cpp \
 	audio_provider_convert.cpp \
+	audio_provider_downmix.cpp \
 	audio_provider_hd.cpp \
 	audio_provider_pcm.cpp \
 	audio_provider_ram.cpp \