diff --git a/classes.py b/classes.py
index df8f4e5..f26e298 100644
--- a/classes.py
+++ b/classes.py
@@ -27,7 +27,7 @@ from .log import *
 
 ### Exceptions
 
-class ProtocolError(Exception):
+class ProtocolError(RuntimeError):
     pass
 
 ### Internal classes (users, servers, channels)
@@ -312,7 +312,11 @@ class Irc():
                               'trying to set up this connection. Please check'
                               ' your configuration file and try again.',
                               self.name)
-            except (socket.error, ProtocolError, ConnectionError) as e:
+            # Note: socket.error, ConnectionError, IOError, etc. are included in OSError since Python 3.3,
+            # so we don't need to explicitly catch them here.
+            # We also catch SystemExit here as a way to abort out connection threads properly, and stop the
+            # IRC connection from freezing instead.
+            except (OSError, RuntimeError, SystemExit) as e:
                 # self.run() or the protocol module it called raised an
                 # exception, meaning we've disconnected!
                 log.error('(%s) Disconnected from IRC: %s: %s',