diff --git a/assetman/managers.py b/assetman/managers.py
index c9f8bc1..909fc8d 100644
--- a/assetman/managers.py
+++ b/assetman/managers.py
@@ -5,7 +5,7 @@
 import functools
 import hashlib
 
-from assetman.tools import get_shard_from_list, _utf8
+from assetman.tools import get_shard_from_list, _unicode
 from assetman.manifest import Manifest
 
 class AssetManager(object):
@@ -46,7 +46,7 @@ def __init__(self, rel_url_text, local=False, include_tag=True, src_path=None, s
         Any extra kwargs will be interpreted as extra HTML params to include
         on the rendered element.
         """
-        self.rel_urls = [_f for _f in _utf8(rel_url_text).split() if _f]
+        self.rel_urls = [_f for _f in _unicode(rel_url_text).split() if _f]
         self.local = local
         self.include_tag = include_tag
         self.src_path = src_path
@@ -100,7 +100,7 @@ def render_attrs(self):
         """Returns this asset block's attrs as an HTML string. Includes a
         leading space.
         """
-        attrs = ' '.join('%s=%r' % (attr, _utf8(val))
+        attrs = ' '.join('%s=%r' % (attr, _unicode(val))
                          for attr, val in self.attrs.items())
         return ' ' + attrs if attrs else ''
 
diff --git a/assetman/tools.py b/assetman/tools.py
index 08c54be..efed01f 100644
--- a/assetman/tools.py
+++ b/assetman/tools.py
@@ -30,6 +30,16 @@ def _utf8(s):
     assert isinstance(s, bytes), "_utf8 expected a str or utf-8 encoded bytes, not %r" % type(s)
     return s
 
+def _unicode(value):
+    """decode utf-8 bytes, returning string"""
+    if isinstance(value, bytes):
+        try:
+            return value.decode("utf-8")
+        except UnicodeDecodeError:
+            raise AssertionError("Invalid encoding. _unicode expected a str or utf-8 encoded bytes")
+    assert isinstance(value, str), "_unicode expected a str or utf-8 encoded bytes, not %r" % type(value)
+    return value
+
 def iter_template_paths(template_dirs, template_ext):
     """Walks each directory in the given list of template directories,
     yielding the path to each template found.