Index: twisted/spread/jelly.py
===================================================================
--- twisted/spread/jelly.py     (revision 12808)
+++ twisted/spread/jelly.py     (working copy)
@@ -164,6 +164,16 @@
     unjellyableRegistry[classname] = unjellyable
     globalSecurity.allowTypes(classname)

+def getUnjellyableForClass(classname):
+    """Lookup and return the registered unjellyable for the classname.
+
+    If no class is registered as an unjellyable, raise an exception.
+    """
+    global unjellyableRegistry
+    classname = _maybeClass(classname)
+    return unjellyableRegistry[classname]
+
+
 def setUnjellyableFactoryForClass(classname, copyFactory):
     """
     Set the factory to construct a remote instance of a type::
Index: twisted/spread/pb.py
===================================================================
--- twisted/spread/pb.py        (revision 12808)
+++ twisted/spread/pb.py        (working copy)
@@ -81,7 +81,7 @@

 # Sibling Imports
 from twisted.spread.interfaces import IJellyable, IUnjellyable
-from jelly import jelly, unjelly, globalSecurity
+from jelly import jelly, unjelly, globalSecurity, getUnjellyableForClass
 import banana

 # Tightly coupled sibling import
@@ -459,8 +459,17 @@
         if isinstance(self.value, failure.Failure):
             state['value'] = failure2Copyable(self.value, self.unsafeTracebacks)
         else:
-            state['value'] = str(self.value) # Exception instance
-        state['type'] = str(self.type) # Exception class
+            try:
+                getUnjellyableForClass(self.type)
+            except:
+                # If the class has no registered unjellyable, save a string
+                # representation of it instead
+                state['value'] = str(self.value)
+            else:
+                # Otherwise save the actual exception instance
+                state['value'] = self.value
+        # Always save a string representation of the type, since it is difficult to jelly types
+        state['type'] = str(self.type)
         if self.unsafeTracebacks:
             io = StringIO.StringIO()
             self.printTraceback(io)