diff --git a/bacnet-stack/ao.c b/bacnet-stack/ao.c
index 99fbca6b..3b5ca663 100644
--- a/bacnet-stack/ao.c
+++ b/bacnet-stack/ao.c
@@ -125,7 +125,7 @@ static float Analog_Output_Present_Value(uint32_t object_instance)
   unsigned i = 0; 
 
   Analog_Output_Init();
-  index = Analog_Output_Index_To_Instance(object_instance);
+  index = Analog_Output_Instance_To_Index(object_instance);
   if (index < MAX_ANALOG_OUTPUTS)
   {
     for (i = 0; i < BACNET_MAX_PRIORITIES; i++)
@@ -373,13 +373,17 @@ void testAnalogOutput(Test * pTest)
   BACNET_OBJECT_TYPE decoded_type = OBJECT_ANALOG_OUTPUT;
   uint32_t decoded_instance = 0;
   uint32_t instance = 123;
+  BACNET_ERROR_CLASS error_class;
+  BACNET_ERROR_CODE error_code;
 
   
   len = Analog_Output_Encode_Property_APDU(
     &apdu[0],
     instance,
     PROP_OBJECT_IDENTIFIER,
-    BACNET_ARRAY_ALL);
+    BACNET_ARRAY_ALL,
+    &error_class,
+    &error_code);
   ct_test(pTest, len != 0);
   len = decode_tag_number_and_value(&apdu[0], &tag_number, &len_value);
   ct_test(pTest, tag_number == BACNET_APPLICATION_TAG_OBJECT_ID);
@@ -391,7 +395,7 @@ void testAnalogOutput(Test * pTest)
   return;
 }
 
-#ifdef TEST_ANALOG_INPUT
+#ifdef TEST_ANALOG_OUTPUT
 int main(void)
 {
     Test *pTest;
diff --git a/bacnet-stack/ao.mak b/bacnet-stack/ao.mak
new file mode 100755
index 00000000..6343403a
--- /dev/null
+++ b/bacnet-stack/ao.mak
@@ -0,0 +1,33 @@
+#Makefile to build test case
+CC      = gcc
+BASEDIR = .
+#CFLAGS  = -Wall -I.
+# -g for debugging with gdb
+#CFLAGS  = -Wall -I. -g
+CFLAGS  = -Wall -I. -Itest -DTEST -DTEST_ANALOG_OUTPUT -g
+
+SRCS = bacdcode.c \
+       bigend.c \
+       ao.c \
+       test/ctest.c
+
+OBJS = ${SRCS:.c=.o}
+
+TARGET = analog_output
+
+all: ${TARGET}
+ 
+${TARGET}: ${OBJS}
+	${CC} -o $@ ${OBJS} 
+
+.c.o:
+	${CC} -c ${CFLAGS} $*.c -o $@
+	
+depend:
+	rm -f .depend
+	${CC} -MM ${CFLAGS} *.c >> .depend
+	
+clean:
+	rm -rf core ${TARGET} $(OBJS) *.bak *.1 *.ini
+
+include: .depend
diff --git a/bacnet-stack/test.sh b/bacnet-stack/test.sh
index 92b13aec..0f45af8d 100755
--- a/bacnet-stack/test.sh
+++ b/bacnet-stack/test.sh
@@ -74,6 +74,11 @@ make -f ai.mak
 ./analog_input >> test.log
 make -f ai.mak clean
 
+make -f ao.mak clean
+make -f ao.mak
+./analog_output >> test.log
+make -f ao.mak clean
+
 make -f wp.mak clean
 make -f wp.mak
 ./writeproperty >> test.log