diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -1221,6 +1221,11 @@ def termwidth():
                 return array.array('h', arri)[1]
             except ValueError:
                 pass
+            except IOError, e: 
+                if e[0] == errno.EINVAL: 
+                    pass 
+                else: 
+                    raise 
     except ImportError:
         pass
     return 80