--- a/mercurial/error.py	Mon Dec 05 21:36:35 2016 +0000
+++ b/mercurial/error.py	Tue Dec 06 14:57:47 2016 +0000
@@ -168,6 +168,9 @@
 class PushRaced(RuntimeError):
     """An exception raised during unbundling that indicate a push race"""
 
+class ProgrammingError(RuntimeError):
+    """Raised if a developer has made some mistake"""
+
 # bundle2 related errors
 class BundleValueError(ValueError):
     """error raised when bundle2 cannot be processed"""