diff --git a/dev_requirements.txt b/dev_requirements.txt
index acb5d77..b00073a 100644
--- a/dev_requirements.txt
+++ b/dev_requirements.txt
@@ -1,5 +1,6 @@
 -r requirements.txt
 
+mock==3.0.5;python_version<"3.3"
 pytest==5.3.1;python_version>="3.5"
 pytest==4.6.6;python_version<"3.5"
 pytest-cov==2.8.1
diff --git a/tests/unit/test_route.py b/tests/unit/test_route.py
new file mode 100644
index 0000000..8c052e8
--- /dev/null
+++ b/tests/unit/test_route.py
@@ -0,0 +1,36 @@
+import pytest
+
+from umodbus.route import DataRule
+
+
+endpoint = lambda slave_id, function_code, address: 0
+
+
+def test_basic_route():
+    rule = DataRule(endpoint, slave_ids=[1], function_codes=[1], addresses=[1])
+    assert rule.match(slave_id=1, function_code=1, address=1)
+    assert not rule.match(slave_id=0, function_code=1, address=1)
+    assert not rule.match(slave_id=1, function_code=0, address=1)
+    assert not rule.match(slave_id=1, function_code=1, address=0)
+
+
+def test_other_iterables():
+    # Other iterable types should work, not just lists
+    rule = DataRule(endpoint,
+                    slave_ids=set([1]), function_codes=[1], addresses=[1])
+    assert rule.match(slave_id=1, function_code=1, address=1)
+
+
+def test_wildcard_slave_id():
+    rule = DataRule(endpoint, slave_ids=None, function_codes=[1], addresses=[1])
+    assert rule.match(slave_id=1, function_code=1, address=1)
+
+
+def test_wildcard_function_code():
+    rule = DataRule(endpoint, slave_ids=[1], function_codes=None, addresses=[1])
+    assert rule.match(slave_id=1, function_code=1, address=1)
+
+
+def test_wildcard_address():
+    rule = DataRule(endpoint, slave_ids=[1], function_codes=[1], addresses=None)
+    assert rule.match(slave_id=1, function_code=1, address=1)
diff --git a/umodbus/route.py b/umodbus/route.py
index b95e6f4..3765e87 100644
--- a/umodbus/route.py
+++ b/umodbus/route.py
@@ -20,9 +20,8 @@ def __init__(self, endpoint, slave_ids, function_codes, addresses):
         self.addresses = addresses
 
     def match(self, slave_id, function_code, address):
-        if slave_id in self.slave_ids and\
-            function_code in self.function_codes and \
-                address in self.addresses:
-                    return True
-
-        return False
+        # A constraint of None matches any value
+        matches = lambda values, v: values is None or v in values
+        return matches(self.slave_ids, slave_id) and \
+               matches(self.function_codes, function_code) and \
+               matches(self.addresses, address)
diff --git a/umodbus/server/__init__.py b/umodbus/server/__init__.py
index 03b598b..f9d4093 100644
--- a/umodbus/server/__init__.py
+++ b/umodbus/server/__init__.py
@@ -19,9 +19,11 @@ def route(self, slave_ids=None, function_codes=None, addresses=None):
         def read_single_bit_values(slave_id, address):
             return random.choise([0, 1])
 
-    :param slave_ids: A list or set with slave id's.
-    :param function_codes: A list or set with function codes.
-    :param addresses: A list or set with addresses.
+    Any argument can be omitted to match any value.
+
+    :param slave_ids: A list (or iterable) of slave ids.
+    :param function_codes: A list (or iterable) of function codes.
+    :param addresses: A list (or iterable) of addresses.
     """
     def inner(f):
         self.route_map.add_rule(f, slave_ids, function_codes, addresses)