diff --git a/app/proguard-rules.pro b/app/proguard-rules.pro
new file mode 100644
index 0000000..d0dbeb7
--- /dev/null
+++ b/app/proguard-rules.pro
@@ -0,0 +1,7 @@
+# Add project specific ProGuard rules here.
+# By default, the flags in this file are appended to flags specified
+# in /home/wlama/bin/android-studio/plugins/android/resources/proguard-android-optimize.txt
+
+-keep class com.abcomm.MainViewModel { *; }
+-keep class com.abcomm.BluetoothService { *; }
+-keep interface com.abcomm.CommunicationProvider { *; }
diff --git a/app/src/main/java/com/abcomm/MainActivity.kt b/app/src/main/java/com/abcomm/MainActivity.kt
index 467e49d..2113521 100644
--- a/app/src/main/java/com/abcomm/MainActivity.kt
+++ b/app/src/main/java/com/abcomm/MainActivity.kt
@@ -37,7 +37,11 @@ class MainActivity : AppCompatActivity() {
     private val viewModel: MainViewModel by viewModels {
         object : ViewModelProvider.Factory {
             override fun <T : ViewModel> create(modelClass: Class<T>): T {
-                return MainViewModel(BluetoothService()) as T
+                if (modelClass.isAssignableFrom(MainViewModel::class.java)) {
+                    @Suppress("UNCHECKED_CAST")
+                    return MainViewModel(BluetoothService()) as T
+                }
+                throw IllegalArgumentException("Unknown ViewModel class")
             }
         }
     }