diff --git a/src/kyupy/stil.py b/src/kyupy/stil.py
index fe714cb..7cacc5b 100644
--- a/src/kyupy/stil.py
+++ b/src/kyupy/stil.py
@@ -40,7 +40,7 @@ class StilFile:
                 unload = {}
                 for so_port in self.so_ports:
                     if so_port in call.parameters:
-                        unload[so_port] = call.parameters[so_port].replace('\n', '')
+                        unload[so_port] = call.parameters[so_port].replace('\n', '').replace('N', '-')
                 if len(capture) > 0:
                     self.patterns.append(ScanPattern(sload, launch, capture, unload))
                     capture = {}
@@ -48,11 +48,11 @@ class StilFile:
                 sload = {}
                 for si_port in self.si_ports:
                     if si_port in call.parameters:
-                        sload[si_port] = call.parameters[si_port].replace('\n', '')
+                        sload[si_port] = call.parameters[si_port].replace('\n', '').replace('N', '-')
             if call.name.endswith('_launch'):
-                launch = dict((k, v.replace('\n', '')) for k, v in call.parameters.items())
+                launch = dict((k, v.replace('\n', '').replace('N', '-')) for k, v in call.parameters.items())
             if call.name.endswith('_capture'):
-                capture = dict((k, v.replace('\n', '')) for k, v in call.parameters.items())
+                capture = dict((k, v.replace('\n', '').replace('N', '-')) for k, v in call.parameters.items())
 
     def _maps(self, c):
         interface = list(c.interface) + [n for n in c.nodes if 'DFF' in n.kind]