diff --git a/src/emu/chan.c b/src/emu/chan.c
index 638aaf4..3b56556 100644
--- a/src/emu/chan.c
+++ b/src/emu/chan.c
@@ -37,7 +37,7 @@ set_dirty(struct chan *chan)
 {
 	if (chan->is_dirty) {
 		/* Already dirty and allowed, no need to do anything */
-		if (chan->allow_dirty_write)
+		if (chan->prop[CHAN_DIRTY_WRITE])
 			return 0;
 
 		err("channel %s already dirty\n", chan->name);
@@ -61,8 +61,8 @@ static int
 check_duplicates(struct chan *chan, struct value *v)
 {
 	/* If duplicates are allowed just skip the check */
-	//if (chan->oflags & CHAN_DUP)
-	//	return 0;
+	if (chan->prop[CHAN_DUPLICATES])
+		return 0;
 
 	if (value_is_equal(&chan->last_value, v)) {
 		err("check_duplicates %s: same value as last_value\n",
@@ -82,7 +82,7 @@ chan_set(struct chan *chan, struct value value)
 		return -1;
 	}
 
-	if (chan->is_dirty && !chan->allow_dirty_write) {
+	if (chan->is_dirty && !chan->prop[CHAN_DIRTY_WRITE]) {
 		err("chan_set %s: cannot modify dirty channel\n",
 				chan->name);
 		return -1;
@@ -122,7 +122,7 @@ chan_push(struct chan *chan, struct value value)
 		return -1;
 	}
 
-	if (chan->is_dirty && !chan->allow_dirty_write) {
+	if (chan->is_dirty && !chan->prop[CHAN_DIRTY_WRITE]) {
 		err("chan_push %s: cannot modify dirty channel\n",
 				chan->name);
 		return -1;
@@ -167,7 +167,7 @@ chan_pop(struct chan *chan, struct value evalue)
 		return -1;
 	}
 
-	if (chan->is_dirty && !chan->allow_dirty_write) {
+	if (chan->is_dirty && !chan->prop[CHAN_DIRTY_WRITE]) {
 		err("chan_pop %s: cannot modify dirty channel\n",
 				chan->name);
 		return -1;
@@ -198,33 +198,25 @@ chan_pop(struct chan *chan, struct value evalue)
 	return 0;
 }
 
-static int
+static void
 get_value(struct chan *chan, struct value *value)
 {
 	if (chan->type == CHAN_SINGLE) {
 		 *value = chan->data.value;
-		 return 0;
+	} else {
+		struct chan_stack *stack = &chan->data.stack;
+		if (stack->n > 0)
+			*value = stack->values[stack->n - 1];
+		else
+			*value = value_null();
 	}
-
-	struct chan_stack *stack = &chan->data.stack;
-	if (stack->n <= 0) {
-		err("get_value %s: channel stack empty\n", chan->name);
-		return -1;
-	}
-
-	*value = stack->values[stack->n - 1];
-
-	return 0;
 }
 
 /** Reads the current value of a channel */
 int
 chan_read(struct chan *chan, struct value *value)
 {
-	if (get_value(chan, value) != 0) {
-		err("chan_read %s: get_value failed\n", chan->name);
-		return -1;
-	}
+	get_value(chan, value);
 
 	return 0;
 }
@@ -238,13 +230,21 @@ chan_flush(struct chan *chan)
 		return -1;
 	}
 
+	get_value(chan, &chan->last_value);
+
 	chan->is_dirty = 0;
 
 	return 0;
 }
 
 void
-chan_dirty_write(struct chan *chan, int allow)
+chan_prop_set(struct chan *chan, enum chan_prop prop, int value)
 {
-	chan->allow_dirty_write = allow;
+	chan->prop[prop] = value;
+}
+
+int
+chan_prop_get(struct chan *chan, enum chan_prop prop)
+{
+	return chan->prop[prop];
 }
diff --git a/src/emu/chan.h b/src/emu/chan.h
index 47bd839..2c84bbd 100644
--- a/src/emu/chan.h
+++ b/src/emu/chan.h
@@ -16,6 +16,12 @@ enum chan_type {
 	CHAN_MAXTYPE,
 };
 
+enum chan_prop {
+	CHAN_DIRTY_WRITE = 0,
+	CHAN_DUPLICATES,
+	CHAN_MAXPROP,
+};
+
 struct chan_stack {
 	int n;
 	struct value values[MAX_CHAN_STACK];
@@ -35,8 +41,7 @@ struct chan {
 	enum chan_type type;
 	union chan_data data;
 	int is_dirty;
-	int allow_dirty_write;
-	struct value err_value;
+	int prop[CHAN_MAXPROP];
 	struct value last_value;
 	chan_cb_t dirty_cb;
 	void *dirty_arg;
@@ -53,7 +58,9 @@ int chan_pop(struct chan *chan, struct value expected);
 int chan_read(struct chan *chan, struct value *value);
 enum chan_type chan_get_type(struct chan *chan);
 int chan_flush(struct chan *chan);
-void chan_dirty_write(struct chan *chan, int allow);
+
+void chan_prop_set(struct chan *chan, enum chan_prop prop, int value);
+int chan_prop_get(struct chan *chan, enum chan_prop prop);
 
 /* Called when it becomes dirty */
 void chan_set_dirty_cb(struct chan *chan, chan_cb_t func, void *arg);
diff --git a/src/emu/mux.c b/src/emu/mux.c
index 0c46cb6..1e7d37e 100644
--- a/src/emu/mux.c
+++ b/src/emu/mux.c
@@ -140,9 +140,9 @@ mux_init(struct mux *mux,
 	}
 
 	/* The output channel must accept multiple writes in the same
-	 * propagation phase, as we may write to the input and select
-	 * channel at the same time. */
-	chan_dirty_write(output, 1);
+	 * propagation phase while the channel is dirty, as we may write to the
+	 * input and select channel at the same time. */
+	chan_prop_set(output, CHAN_DIRTY_WRITE, 1);
 
 	memset(mux, 0, sizeof(struct mux_input));
 	mux->select = select;
diff --git a/test/unit/chan.c b/test/unit/chan.c
index 6e17f82..ab49a98 100644
--- a/test/unit/chan.c
+++ b/test/unit/chan.c
@@ -18,7 +18,7 @@ test_dirty(void)
 	if (chan_flush(&chan) != 0)
 		die("chan_flush failed\n");
 
-	chan_dirty_write(&chan, 1);
+	chan_prop_set(&chan, CHAN_DIRTY_WRITE, 1);
 
 	if (chan_set(&chan, value_int64(3)) != 0)
 		die("chan_set failed\n");
@@ -71,6 +71,30 @@ test_single(void)
 		die("chan_read returned unexpected value\n");
 }
 
+static void
+test_duplicate(void)
+{
+	struct chan chan;
+	chan_init(&chan, CHAN_SINGLE, "testchan");
+
+	if (chan_set(&chan, value_int64(1)) != 0)
+		die("chan_set failed\n");
+
+	if (chan_flush(&chan) != 0)
+		die("chan_flush failed\n");
+
+	/* Attempt to write the same value again */
+	if (chan_set(&chan, value_int64(1)) == 0)
+		die("chan_set didn't fail\n");
+
+	/* Now enable duplicates */
+	chan_prop_set(&chan, CHAN_DUPLICATES, 1);
+
+	/* Then it should allow writting the same value */
+	if (chan_set(&chan, value_int64(1)) != 0)
+		die("chan_set failed\n");
+}
+
 //static void
 //test_stack(void)
 //{
@@ -132,6 +156,7 @@ int main(void)
 {
 	test_single();
 	test_dirty();
+	test_duplicate();
 	//test_stack();
 	return 0;
 }