diff --git a/viewmodel/build.gradle b/viewmodel/build.gradle
index d664bd4..1602732 100644
--- a/viewmodel/build.gradle
+++ b/viewmodel/build.gradle
@@ -19,6 +19,7 @@ android {
         minSdk 14
         targetSdk libs.versions.targetSdk.get().toInteger()
         testInstrumentationRunner 'androidx.test.runner.AndroidJUnitRunner'
+        consumerProguardFiles 'proguard-rules.pro'
     }
 }
 
diff --git a/viewmodel/proguard-rules.pro b/viewmodel/proguard-rules.pro
new file mode 100644
index 0000000..adea95c
--- /dev/null
+++ b/viewmodel/proguard-rules.pro
@@ -0,0 +1,11 @@
+# lich-viewmodel keys ViewModelStore entries by
+# "lich:" + factory.javaClass.canonicalName, so every ViewModelFactory subclass
+# must remain a distinct, stably-named class. Without this rule, R8 full mode
+# horizontally merges the stateless companion factories into a single class,
+# making all keys collide and returning the wrong ViewModel (ClassCastException).
+#
+# -keepnames (= -keep,allowshrinking) only pins the class *name*: it prevents
+# renaming and class merging, keeps no members, and still allows unused
+# factories to be removed.
+#
+-keepnames class * extends com.linecorp.lich.viewmodel.ViewModelFactory