diff --git a/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsFrameLayout.kt b/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsFrameLayout.kt
index c9cf51f..7a4ba26 100644
--- a/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsFrameLayout.kt
+++ b/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsFrameLayout.kt
@@ -13,7 +13,7 @@ import android.widget.FrameLayout
  * physics component.
  */
 @Suppress("unused")
-class PhysicsFrameLayout : FrameLayout {
+open class PhysicsFrameLayout : FrameLayout {
 
     lateinit var physics: Physics
 
diff --git a/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsLinearLayout.kt b/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsLinearLayout.kt
index 71d2cf4..47ea4ee 100644
--- a/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsLinearLayout.kt
+++ b/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsLinearLayout.kt
@@ -13,7 +13,7 @@ import android.widget.LinearLayout
  * physics component.
  */
 @Suppress("unused")
-class PhysicsLinearLayout : LinearLayout {
+open class PhysicsLinearLayout : LinearLayout {
 
     lateinit var physics: Physics
 
diff --git a/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsRelativeLayout.kt b/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsRelativeLayout.kt
index f349055..dbb35c0 100644
--- a/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsRelativeLayout.kt
+++ b/physicslayout/src/main/java/com/jawnnypoo/physicslayout/PhysicsRelativeLayout.kt
@@ -13,7 +13,7 @@ import android.widget.RelativeLayout
  * physics component.
  */
 @Suppress("unused")
-class PhysicsRelativeLayout : RelativeLayout {
+open class PhysicsRelativeLayout : RelativeLayout {
 
     lateinit var physics: Physics