diff -r e8f49b32e95b -r 41d2555141ea hgext/evolve.py
--- a/hgext/evolve.py	Wed Aug 27 17:12:01 2014 +0200
+++ b/hgext/evolve.py	Wed Aug 27 17:24:40 2014 +0200
@@ -2396,7 +2396,7 @@
     def length(self):
         return len(self.getvalue())
 
-    def read(self, size):
+    def read(self, size=None):
         obsexcprg(self.ui, self.tell(), unit="bytes", total=self.length)
         return StringIO.read(self, size)