--- src/plugin_zencoding/zencoding/__init__.py
+++ src/plugin_zencoding/zencoding/__init__.py
@@ -26,7 +26,7 @@ def action(name=None, action_func=None):
 		__actions[name] = action_func
 		return action_func
 	else:
-		raise "Unsupported arguments to Zen Action: (%r, %r)", (name, action_func)
+		raise ValueError("Unsupported arguments to Zen Action: (%r, %r)" % (name, action_func))
 
 def action_function(func):
 	__actions[getattr(func, "_decorated_function", func).__name__] = func
@@ -51,7 +51,7 @@ def filter(name=None, filter_func=None):
 		__filters[name] = filter_func
 		return filter_func
 	else:
-		raise "Unsupported arguments to Zen Filter: (%r, %r)", (name, filter_func)
+		raise ValueError("Unsupported arguments to Zen Filter: (%r, %r)" % (name, filter_func))
 
 def filter_function(func):
 	__filters[getattr(func, "_decorated_function", func).__name__] = func
@@ -147,4 +147,4 @@ def wrap_with_abbreviation(abbr, text, s
 		utils.apply_filters(tree, syntax, profile, tree_root.filters)
 		return utils.replace_variables(tree.to_string())
 	
-	return None
\ No newline at end of file
+	return None
--- src/plugin_zencoding/zencoding/parser/xml.py
+++ src/plugin_zencoding/zencoding/parser/xml.py
@@ -137,7 +137,7 @@ class StringStream(object):
 		"""
 		if not self.ensure_chars():
 			if len(self.accum) > 0:
-				raise "End of stringstream reached without emptying buffer ('" + self.accum + "')."
+				raise Exception("End of stringstream reached without emptying buffer ('" + self.accum + "').")
 			else:
 				raise StopIteration