diff --git a/blockcanary-android/src/main/java/com/github/moduth/blockcanary/BlockCanary.java b/blockcanary-android/src/main/java/com/github/moduth/blockcanary/BlockCanary.java
index cbb2cb0..8814a79 100644
--- a/blockcanary-android/src/main/java/com/github/moduth/blockcanary/BlockCanary.java
+++ b/blockcanary-android/src/main/java/com/github/moduth/blockcanary/BlockCanary.java
@@ -25,7 +25,7 @@
  *
  * @author markzhai on 2015/9/25.
  */
-public class BlockCanary {
+public final class BlockCanary {
 
     private static final String TAG = "BlockCanary";
 
diff --git a/blockcanary-core/src/main/java/com/github/moduth/blockcanary/log/Block.java b/blockcanary-core/src/main/java/com/github/moduth/blockcanary/log/Block.java
index 5208306..4592501 100644
--- a/blockcanary-core/src/main/java/com/github/moduth/blockcanary/log/Block.java
+++ b/blockcanary-core/src/main/java/com/github/moduth/blockcanary/log/Block.java
@@ -32,7 +32,7 @@
 /**
  * @author markzhai on 15/9/27.
  */
-public class Block {
+public final class Block {
 
     private static final String TAG = "Block";
 
diff --git a/blockcanary-no-op/src/main/java/com/github/moduth/blockcanary/BlockCanary.java b/blockcanary-no-op/src/main/java/com/github/moduth/blockcanary/BlockCanary.java
index b5565bd..7f7cd70 100644
--- a/blockcanary-no-op/src/main/java/com/github/moduth/blockcanary/BlockCanary.java
+++ b/blockcanary-no-op/src/main/java/com/github/moduth/blockcanary/BlockCanary.java
@@ -18,7 +18,7 @@
 /**
  * No-op implementation.
  */
-public class BlockCanary {
+public final class BlockCanary {
 
     private static BlockCanary sInstance = null;