--- a/configmix/config.py	Fri Dec 31 21:24:16 2021 +0100
+++ b/configmix/config.py	Sat Jan 01 18:01:32 2022 +0100
@@ -31,10 +31,11 @@
 from .compat import u, uchr, n, str_and_u, PY2
 from .constants import REF_NAMESPACE, NONE_FILTER, EMPTY_FILTER
 try:
-    from ._speedups import fast_unquote, fast_pathstr2path
+    from ._speedups import fast_unquote, fast_pathstr2path, _fast_split_ns
 except ImportError:
     fast_unquote = None
     fast_pathstr2path = None
+    _fast_split_ns = None
 
 
 _MARKER = object()
@@ -362,7 +363,7 @@
     pathstr2path = py_pathstr2path
 
 
-def _split_ns(varname):
+def _py_split_ns(varname):
     """Split the variable name string `varname` into the namespace and
     the namespace-specific name
 
@@ -371,6 +372,9 @@
              namespace-specific (variable-)name
     :rtype: tuple(str or None, str)
 
+    .. note:: The returned namespace may be an empty string if the namespace
+              separator is found.
+
     """
     ns, sep, rest = varname.partition(_NS_SEPARATOR)
     if sep:
@@ -379,6 +383,12 @@
         return (None, ns)
 
 
+if _fast_split_ns:
+    _split_ns = _fast_split_ns
+else:
+    _split_ns = _py_split_ns
+
+
 def _split_filters(varname):
     """Split off the filter part from the `varname` string