@@ -845,7 +845,7 @@ def append(self, other):
             (other.noutputs, other.ninputs, -1),
         )
 
-        return FRD(new_fresp, self.omega, smooth=(self.ifunc is not None))
+        return FRD(new_fresp, self.omega, smooth=(self._ifunc is not None))
 
     # Plotting interface
     def plot(self, plot_type=None, *args, **kwargs):
Original file line number	Diff line number	Diff line change
`@@ -845,7 +845,7 @@ def append(self, other):`
`845`	`845`	`(other.noutputs, other.ninputs, -1),`
`846`	`846`	`)`
`847`	`847`
`848`		`- return FRD(new_fresp, self.omega, smooth=(self.ifunc is not None))`
	`848`	`+ return FRD(new_fresp, self.omega, smooth=(self._ifunc is not None))`
`849`	`849`
`850`	`850`	`# Plotting interface`
`851`	`851`	`def plot(self, plot_type=None, args, *kwargs):`