diff --git a/bonobo/execution/contexts/graph.py b/bonobo/execution/contexts/graph.py
index 2828592..ffc9dcc 100644
--- a/bonobo/execution/contexts/graph.py
+++ b/bonobo/execution/contexts/graph.py
@@ -149,10 +149,10 @@ class GraphExecutionContext(BaseContext):
         for plugin_context in self.plugins:
             plugin_context.unregister()
 
-
     @property
     def xstatus(self):
         """
         UNIX-like exit status, only coherent if the context has stopped.
+
         """
-        return max(node.xstatus for node in self.nodes)
+        return max(node.xstatus for node in self.nodes) if len(self.nodes) else 0
diff --git a/bonobo/execution/contexts/node.py b/bonobo/execution/contexts/node.py
index b5884a7..44476f0 100644
--- a/bonobo/execution/contexts/node.py
+++ b/bonobo/execution/contexts/node.py
@@ -302,9 +302,8 @@ class NodeExecutionContext(BaseContext, WithStatistics):
                     input_bag = self._input_type(*input_bag)
             except Exception as exc:
                 raise UnrecoverableTypeError(
-                    'Input type changed to incompatible type between calls to {!r}.\nGot {!r} which is not of type {!r}.'.format(
-                        self.wrapped, input_bag, self._input_type
-                    )
+                    'Input type changed to incompatible type between calls to {!r}.\nGot {!r} which is not of type {!r}.'.
+                    format(self.wrapped, input_bag, self._input_type)
                 ) from exc
 
         # Store or check input length, which is a soft fallback in case we're just using tuples