diff --git a/dav_events/config.py b/dav_events/config.py
index de43024..34db588 100644
--- a/dav_events/config.py
+++ b/dav_events/config.py
@@ -20,7 +20,7 @@ ADDITIONAL_COSTS_MAX_LENGTH = COMMON_CHAR_FIELD_LENGTH
 
 
 class FieldInitial(object):
-    _constraint_re = re.compile(r'^(?P<field>[a-z_]+)(?P<op>[=]+)(?P<value>.*)$')
+    _constraint_re = re.compile(r'^(?P<field>[a-z_]+)(?P<op>==)(?P<value>[^= ].*)?$')
 
     def __init__(self, *args):
         self._tuples = []
@@ -61,8 +61,10 @@ class FieldInitial(object):
                     if c_field not in parameters:
                         logger.error('FieldInitial: Invalid field: \'%s\'', sub_constraint)
                         continue
-                    c_op = c.group('op')
                     c_value = c.group('value')
+                    if c_value is None:
+                        c_value = ''
+                    c_op = c.group('op')
                     if c_op == '==':
                         if parameters[c_field] == c_value:
                             match = True
@@ -70,7 +72,7 @@ class FieldInitial(object):
                         else:
                             match = False
                             break
-                    else:
+                    else:  # pragma: no cover
                         logger.error('FieldInitial: Invalid operator: \'%s\'', sub_constraint)
                         continue
                 else:
diff --git a/dav_events/tests/test_config.py b/dav_events/tests/test_config.py
index 7eaaca3..02142a7 100644
--- a/dav_events/tests/test_config.py
+++ b/dav_events/tests/test_config.py
@@ -83,8 +83,10 @@ class FieldInitialTestCase(TestCase):
     def test_invalid_constraints(self):
         invalid_constraints = (
             'sport',            # Not in <key><operator><value> form
-            'sport ==hiking'    # Blanks before operator
-            'sport== hiking'    # Blanks after operator
+            'sport ==hiking',   # Blank before operator
+            'sport== hiking',   # Blank after operator
+            'sport=hiking',     # Invalid operator
+            'sport===hiking',   # Invalid operator
             'sport!=hiking',    # Invalid operator
             '==hiking',         # Missing key
         )