diff --git a/elementpath/xpath2/xpath2_functions.py b/elementpath/xpath2/xpath2_functions.py
index 3e8a2e32..3889a965 100644
--- a/elementpath/xpath2/xpath2_functions.py
+++ b/elementpath/xpath2/xpath2_functions.py
@@ -19,6 +19,7 @@
 import unicodedata
 from copy import copy
 from decimal import Decimal, DecimalException
+from string import ascii_letters
 from urllib.parse import urlsplit, quote as urllib_quote
 
 from ..datatypes import QNAME_PATTERN, DateTime10, DateTime, Date10, Date, \
@@ -35,6 +36,11 @@
 method = XPath2Parser.method
 function = XPath2Parser.function
 
+
+def is_local_url_scheme(scheme):
+    return scheme in ('', 'file') or len(scheme) == 1 and scheme in ascii_letters
+
+
 ###
 # Sequence types (allowed only for type checking in treat-as/instance-of statements)
 function('empty-sequence', nargs=0, label='sequence type')
@@ -1321,7 +1327,8 @@ def evaluate(self, context=None):
         except (KeyError, TypeError):
             if self.symbol == 'doc':
                 url_parts = urlsplit(uri)
-                if url_parts.scheme in ('', 'file') and os.path.isdir(url_parts.path.lstrip(':')):
+                if is_local_url_scheme(url_parts.scheme) \
+                        and os.path.isdir(url_parts.path.lstrip(':')):
                     raise self.error('FODC0005', 'document URI is a directory')
                 raise self.error('FODC0002')
             return False
@@ -1360,7 +1367,7 @@ def evaluate(self, context=None):
             collection = context.collections[uri]
         except (KeyError, TypeError):
             url_parts = urlsplit(uri)
-            if url_parts.scheme in ('', 'file') and \
+            if is_local_url_scheme(url_parts.scheme) and \
                     not url_parts.path.startswith(':') and url_parts.path.endswith('/'):
                 raise self.error('FODC0003', 'collection URI is a directory')
             raise self.error('FODC0002', '{!r} collection not found'.format(uri)) from None
diff --git a/tests/test_xpath2_parser.py b/tests/test_xpath2_parser.py
index 71f33c07..bb6f6934 100644
--- a/tests/test_xpath2_parser.py
+++ b/tests/test_xpath2_parser.py
@@ -21,6 +21,7 @@
 #
 import unittest
 import io
+import locale
 import os
 from decimal import Decimal
 from textwrap import dedent
@@ -1083,8 +1084,12 @@ def test_default_collection_type_argument(self):
                          "invalid sequence type for default_collection_type argument")
 
     def test_default_collation_argument(self):
-        self.assertEqual(self.parser.__class__().default_collation,
-                         "http://www.w3.org/2005/xpath-functions/collation/codepoint")
+        default_locale = locale.getdefaultlocale()
+        collation = '.'.join(default_locale) if default_locale[1] else default_locale[0]
+
+        if collation == 'en_US.UTF-8':
+            collation = "http://www.w3.org/2005/xpath-functions/collation/codepoint"
+        self.assertEqual(self.parser.__class__().default_collation, collation)
 
         parser = self.parser.__class__(default_collation='it_IT.UTF-8')
         self.assertEqual(parser.default_collation, 'it_IT.UTF-8')