diff --git a/citext/__init__.py b/citext/__init__.py
index b9c4bd9..849f628 100644
--- a/citext/__init__.py
+++ b/citext/__init__.py
@@ -12,6 +12,7 @@
 class CIText(types.Concatenable, types.UserDefinedType):
     # This is copied from the `literal_processor` of sqlalchemy's own `String`
     # type.
+    cache_ok = True
     def literal_processor(self, dialect):
         def process(value):
             value = value.replace("'", "''")
diff --git a/requirements.txt b/requirements.txt
index 10e5582..0705143 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1 +1,2 @@
-SQLAlchemy>=0.6
\ No newline at end of file
+SQLAlchemy>=0.6
+psycopg2
\ No newline at end of file
diff --git a/setup.py b/setup.py
index 295eee2..078a8c8 100644
--- a/setup.py
+++ b/setup.py
@@ -26,6 +26,7 @@
     url='https://github.com/mahmoudimus/sqlalchemy-citext',
     install_requires=[
         'SQLAlchemy>=0.6',
+        'psycopg2'
     ],
     test_suite='tests',
     license='BSD',