diff --git a/libao2/Makefile b/libao2/Makefile
index d30aeb1fe1..a3398d9e8e 100644
--- a/libao2/Makefile
+++ b/libao2/Makefile
@@ -8,7 +8,7 @@ SRCS=afmt.c audio_out.c ao_mpegpes.c ao_null.c ao_pcm.c ao_plugin.c pl_delay.c p
 
 OBJS=$(SRCS:.c=.o)
 
-CFLAGS  = $(OPTFLAGS) -I. -I.. $(ARTS_INC) $(SDL_INC) $(X11_INC) $(EXTRA_INC) $(DXR2_INC) $(DVB_INC)
+CFLAGS  = $(OPTFLAGS) -I. -I.. $(ARTS_INC) $(ESD_INC) $(SDL_INC) $(X11_INC) $(EXTRA_INC) $(DXR2_INC) $(DVB_INC)
 
 .SUFFIXES: .c .o