diff --git a/brian2/groups/group.py b/brian2/groups/group.py
index 859ba7d16..f9dcdb8fa 100644
--- a/brian2/groups/group.py
+++ b/brian2/groups/group.py
@@ -101,7 +101,7 @@ def __getattr__(self, name):
     def __setattr__(self, name, val):
         # attribute access is switched off until this attribute is created by
         # _enable_group_attributes
-        if not hasattr(self, '_group_attribute_access_active'):
+        if not hasattr(self, '_group_attribute_access_active') or name in self.__dict__:
             object.__setattr__(self, name, val)
         elif name in self.variables:
             var = self.variables[name]
diff --git a/brian2/synapses/synapses.py b/brian2/synapses/synapses.py
index 971c43904..8d3f97bce 100644
--- a/brian2/synapses/synapses.py
+++ b/brian2/synapses/synapses.py
@@ -3,6 +3,7 @@
 import weakref
 import itertools
 import re
+import bisect
 
 import numpy as np
 
@@ -210,14 +211,20 @@ def before_run(self, namespace):
                                                            )
         self.updaters.insert(0, self.pushspikes_codeobj.get_updater())
         #self.updaters.insert(0, SynapticPathwayUpdater(self))
-    
+
     def push_spikes(self):
         # Push new spikes into the queue
         spikes = self.source.spikes
+        # Make use of the fact that the spikes list is sorted for faster
+        # subgroup handling
+        start = self.spikes_start
+        start_idx = bisect.bisect_left(spikes, start)
+        stop_idx = bisect.bisect_left(spikes, self.spikes_stop, lo=start_idx)
+        spikes = spikes[start_idx:stop_idx]
+        synapse_indices = self.synapse_indices
         if len(spikes):
-            indices = np.concatenate([self.synapse_indices[spike - self.spikes_start][:]
-                                      for spike in spikes
-                                      if self.spikes_start <= spike < self.spikes_stop]).astype(np.int32)
+            indices = np.concatenate([synapse_indices[spike - start][:]
+                                      for spike in spikes]).astype(np.int32)
 
             if len(indices):
                 if len(self._delays) > 1: