diff --git a/cecil/core/__init__.py b/cecil/core/__init__.py
index 0153021..743cab4 100644
--- a/cecil/core/__init__.py
+++ b/cecil/core/__init__.py
@@ -13,13 +13,17 @@ except NameError:
 	unicode = str
 
 def ascii(s):
-	if isinstance(s, unicode):
+    if isinstance(s, bytes):
+        return s
+	elif isinstance(s, unicode):
 		return s.encode(u'ascii')
 	else:
 		return str(s)
 
 def utf8(s):
-	if isinstance(s, unicode):
+    if isinstance(s, bytes):
+        return s
+	elif isinstance(s, unicode):
 		return s.encode(u'utf-8')
 	else:
 		return str(s)