diff --git a/compiler/custom/nand2_dec.py b/compiler/custom/nand2_dec.py
index 98992f42..893bb34f 100644
--- a/compiler/custom/nand2_dec.py
+++ b/compiler/custom/nand2_dec.py
@@ -70,3 +70,7 @@ class nand2_dec(design.design):
         """
         self.add_graph_edges(graph, port_nets)
 
+    def is_non_inverting(self):
+        """Return input to output polarity for module"""
+
+        return False
diff --git a/compiler/custom/nand3_dec.py b/compiler/custom/nand3_dec.py
index 34890a9c..a887e38f 100644
--- a/compiler/custom/nand3_dec.py
+++ b/compiler/custom/nand3_dec.py
@@ -70,3 +70,7 @@ class nand3_dec(design.design):
         """
         self.add_graph_edges(graph, port_nets)
 
+    def is_non_inverting(self):
+        """Return input to output polarity for module"""
+
+        return False
diff --git a/compiler/custom/nand4_dec.py b/compiler/custom/nand4_dec.py
index d89dc926..d3b6491d 100644
--- a/compiler/custom/nand4_dec.py
+++ b/compiler/custom/nand4_dec.py
@@ -70,3 +70,7 @@ class nand4_dec(design.design):
         """
         self.add_graph_edges(graph, port_nets)
 
+    def is_non_inverting(self):
+        """Return input to output polarity for module"""
+
+        return False