diff --git a/silverberg/marshal.py b/silverberg/marshal.py
index 6dc05e9..330f538 100644
--- a/silverberg/marshal.py
+++ b/silverberg/marshal.py
@@ -42,11 +42,19 @@
 
 
 def prepare(query, params):
-    # For every match of the form ":param_name", call marshal
-    # on kwargs['param_name'] and replace that section of the query
-    # with the result
-    new, count = re.subn(_param_re,
-                         lambda m: marshal(params[m.group(1)[1:]]), query)
+    """
+    For every match of the form ":param_name", call marshal
+    on kwargs['param_name'] and replace that section of the query
+    with the result
+    """
+    def repl(match):
+        name = match.group(1)[1:]
+        if name in params:
+            return marshal(params[name])
+        return ":%s" % name
+
+    new, count = re.subn(_param_re, repl, query)
+
     if len(params) > count:
         raise cql.ProgrammingError("More keywords were provided "
                                    "than parameters")
diff --git a/silverberg/test/test_marshal.py b/silverberg/test/test_marshal.py
index 6a2d31e..f1b324a 100644
--- a/silverberg/test/test_marshal.py
+++ b/silverberg/test/test_marshal.py
@@ -24,7 +24,21 @@
 
 from twisted.trial.unittest import TestCase
 
-from silverberg.marshal import marshal, unmarshal_timestamp, unmarshal_int, unmarshal_initializable_int
+from silverberg.marshal import marshal, unmarshal_timestamp, unmarshal_int, \
+    unmarshal_initializable_int, prepare
+
+
+class StatementPreparation(TestCase):
+    """
+    Test preparint a query with optional parameters.
+    """
+
+    def test_prepare(self):
+        result = prepare("string :with a colon :with", {'with': 'value'})
+        self.assertEqual(result, "string 'value' a colon 'value'")
+
+        result = prepare("string :with a colon :with", {})
+        self.assertEqual(result, "string :with a colon :with")
 
 
 class MarshallingUnmarshallingDatetime(TestCase):