diff --git a/pySim/exceptions.py b/pySim/exceptions.py
index 24aff854..c6a81a13 100644
--- a/pySim/exceptions.py
+++ b/pySim/exceptions.py
@@ -53,8 +53,8 @@ class SwMatchError(Exception):
         self.rs = rs
 
     def __str__(self):
-        if self.rs:
-            r = self.rs.interpret_sw(self.sw_actual)
+        if self.rs and self.rs.lchan[0]:
+            r = self.rs.lchan[0].interpret_sw(self.sw_actual)
             if r:
                 return "SW match failed! Expected %s and got %s: %s - %s" % (self.sw_expected, self.sw_actual, r[0], r[1])
         return "SW match failed! Expected %s and got %s." % (self.sw_expected, self.sw_actual)