1 files changed, 4 insertions, 0 deletions
diff --git a/wcsutil/instruments.py b/wcsutil/instruments.py
index 4491079..6d41e2a 100644
--- a/wcsutil/instruments.py
+++ b/wcsutil/instruments.py
@@ -105,6 +105,10 @@ class ACSWCS(InstrWCS):
         except KeyError:
             print 'ERROR: Detector kw not found.\n'
             raise
+        except TypeError:
+            #this is the case of creating a default HSTWCS object by 
+            #providing 'instrument' and 'detector'
+            pass
     
     def set_parity(self):
         parity = {'WFC':[[1.0,0.0],[0.0,-1.0]],