diff --git a/rtio/sed/output_network.py b/rtio/sed/output_network.py
index 3905a78..932ef18 100644
--- a/rtio/sed/output_network.py
+++ b/rtio/sed/output_network.py
@@ -134,18 +134,21 @@ class OutputNetwork(Elaboratable):
                 for node in self.output:
                     with m.If(node.replace_occured):
                         m.d.comb += replacement_occurred.eq(1)
-                nodes_unique = Signal(reset=1)
+                channels_unique = Signal(reset=1)
                 for node1 in range(len(self.input)):
                     for node2 in range(node1):
-                        k1 = Cat(Past(self.input[node1].payload.channel, clocks=network_latency), ~Past(self.input[node1].valid, clocks=network_latency))
-                        k2 = Cat(Past(self.input[node2].payload.channel, clocks=network_latency), ~Past(self.input[node2].valid, clocks=network_latency))
+                        k1 = Past(self.input[node1].payload.channel, clocks=network_latency)
+                        k2 = Past(self.input[node2].payload.channel, clocks=network_latency)
                         with m.If(k1 == k2):
-                            m.d.comb += nodes_unique.eq(0)
+                            m.d.comb += channels_unique.eq(0)
                 # If there are no replacements then:
-                # - All input data are unique
-                # - They all make it through the sorting network
+                # - (Input) channel numbers are unique
+                # - All outputs are valid
+                # - All inputs make it through the sorting network
                 with m.If(~replacement_occurred):
-                    m.d.comb += Assert(nodes_unique)
+                    m.d.comb += Assert(channels_unique)
+                    for node in self.output:
+                        m.d.comb += Assert(node.valid)
                     for input_node in self.input:
                         appeared = Signal()
                         for output_node in self.output:
@@ -164,25 +167,24 @@ class OutputNetwork(Elaboratable):
                             with m.If(match):
                                 m.d.comb += appeared.eq(1)
                         m.d.comb += Assert(appeared)
-                # Otherwise, TODO
-
-            with m.If(f_output_valid):
-                nodes_unique = Signal(reset=1)
-                for node1 in range(len(self.input)):
-                    for node2 in range(node1):
-                        k1 = Cat(Past(self.input[node1].payload.channel, clocks=network_latency), ~Past(self.input[node1].valid, clocks=network_latency))
-                        k2 = Cat(Past(self.input[node2].payload.channel, clocks=network_latency), ~Past(self.input[node2].valid, clocks=network_latency))
-                        with m.If(k1 == k2):
-                            m.d.comb += nodes_unique.eq(0)
-                replacement_occurred = Signal()
-                for output_node in self.output:
-                    with m.If(output_node.replace_occured):
-                        m.d.comb += replacement_occurred.eq(1)
-                # If the valid bit / channel no. combinations of all input data
-                # are unique then there should be no replacements
-                with m.If(nodes_unique):
-                    m.d.comb += Assert(~replacement_occurred)
-                # Otherwise, TODO
+                # Otherwise, if there are replacements:
+                # - Channel numbers are not unique
+                # - Not all outputs are valid
+                # - All channel numbers in the input appear somewhere as a
+                #   valid output
+                with m.Else():
+                    m.d.comb += Assert(~channels_unique)
+                    all_valid = Signal(reset=1)
+                    for node in self.output:
+                        with m.If(~node.valid):
+                            m.d.comb += all_valid.eq(0)
+                    m.d.comb += Assert(~all_valid)
+                    for input_node in self.input:
+                        appeared_valid = Signal()
+                        for output_node in self.output:
+                            with m.If((Past(input_node.payload.channel, clocks=network_latency) == output_node.payload.channel) & output_node.valid):
+                                m.d.comb += appeared_valid.eq(1)
+                        m.d.comb += Assert(appeared_valid)
 
     def elaborate(self, platform):
         return self.m