diff -r de5c9d0e02ea -r b445a3f00528 mercurial/error.py
--- a/mercurial/error.py	Tue Apr 11 14:54:12 2017 -0700
+++ b/mercurial/error.py	Tue Apr 11 14:54:12 2017 -0700
@@ -122,6 +122,12 @@
 class RequirementError(RepoError):
     """Exception raised if .hg/requires has an unknown entry."""
 
+class StdioError(IOError):
+    """Raised if I/O to stdout or stderr fails"""
+
+    def __init__(self, err):
+        IOError.__init__(self, err.errno, err.strerror)
+
 class UnsupportedMergeRecords(Abort):
     def __init__(self, recordtypes):
         from .i18n import _