diff --git a/TelegramBotBase/States/JSONStateMachine.cs b/TelegramBotBase/States/JSONStateMachine.cs
index d8995be..7035692 100644
--- a/TelegramBotBase/States/JSONStateMachine.cs
+++ b/TelegramBotBase/States/JSONStateMachine.cs
@@ -36,7 +36,7 @@ namespace TelegramBotBase.States
 
             this.FallbackStateForm = fallbackStateForm;
 
-            if (!this.FallbackStateForm.IsSubclassOf(typeof(FormBase)))
+            if (this.FallbackStateForm != null && !this.FallbackStateForm.IsSubclassOf(typeof(FormBase)))
             {
                 throw new ArgumentException("FallbackStateForm is not a subclass of FormBase");
             }
diff --git a/TelegramBotBase/States/SimpleJSONStateMachine.cs b/TelegramBotBase/States/SimpleJSONStateMachine.cs
index 0b6e9e5..faba2af 100644
--- a/TelegramBotBase/States/SimpleJSONStateMachine.cs
+++ b/TelegramBotBase/States/SimpleJSONStateMachine.cs
@@ -36,7 +36,7 @@ namespace TelegramBotBase.States
 
             this.FallbackStateForm = fallbackStateForm;
 
-            if (!this.FallbackStateForm.IsSubclassOf(typeof(FormBase)))
+            if (this.FallbackStateForm != null && !this.FallbackStateForm.IsSubclassOf(typeof(FormBase)))
             {
                 throw new ArgumentException("FallbackStateForm is not a subclass of FormBase");
             }
diff --git a/TelegramBotBase/States/XMLStateMachine.cs b/TelegramBotBase/States/XMLStateMachine.cs
index 76fe5bd..2542f6a 100644
--- a/TelegramBotBase/States/XMLStateMachine.cs
+++ b/TelegramBotBase/States/XMLStateMachine.cs
@@ -35,7 +35,7 @@ namespace TelegramBotBase.States
 
             this.FallbackStateForm = fallbackStateForm;
 
-            if (!this.FallbackStateForm.IsSubclassOf(typeof(FormBase)))
+            if (this.FallbackStateForm != null && !this.FallbackStateForm.IsSubclassOf(typeof(FormBase)))
             {
                 throw new ArgumentException("FallbackStateForm is not a subclass of FormBase");
             }