diff --git a/src/main/java/typewriter/rdb/ConnectionPool.java b/src/main/java/typewriter/rdb/ConnectionPool.java
index 601c9b9d..2ca6f584 100644
--- a/src/main/java/typewriter/rdb/ConnectionPool.java
+++ b/src/main/java/typewriter/rdb/ConnectionPool.java
@@ -40,7 +40,7 @@
 import kiss.I;
 import kiss.WiseSupplier;
 
-public class ConnectionPool implements WiseSupplier<Connection> {
+class ConnectionPool implements WiseSupplier<Connection> {
 
     /** The cached connections for each url. */
     private static final Map<String, Connection> SINGLETONS = new ConcurrentHashMap();
diff --git a/src/main/java/typewriter/rdb/RDBConstraint.java b/src/main/java/typewriter/rdb/RDBConstraint.java
index f97d1983..ffac1545 100644
--- a/src/main/java/typewriter/rdb/RDBConstraint.java
+++ b/src/main/java/typewriter/rdb/RDBConstraint.java
@@ -26,7 +26,7 @@
 /**
  * {@link Constraint} for mongdb.
  */
-public abstract class RDBConstraint<V, Self> implements Constraint<V, Self> {
+abstract class RDBConstraint<V, Self> implements Constraint<V, Self> {
 
     /** The name of target property. */
     protected final String propertyName;
diff --git a/src/main/java/typewriter/rdb/RDBQuery.java b/src/main/java/typewriter/rdb/RDBQuery.java
index e1c63c57..e6f893d9 100644
--- a/src/main/java/typewriter/rdb/RDBQuery.java
+++ b/src/main/java/typewriter/rdb/RDBQuery.java
@@ -55,7 +55,7 @@
 /**
  * {@link Queryable} for RDB.
  */
-public class RDBQuery<M extends Identifiable> implements Queryable<M, RDBQuery<M>> {
+class RDBQuery<M extends Identifiable> implements Queryable<M, RDBQuery<M>> {
 
     /** The all constraint set. */
     protected final List<RDBConstraint<?, ?>> constraints = new ArrayList();