diff --git a/build.gradle.kts b/build.gradle.kts
index 533bb62..b3f01ac 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -6,6 +6,6 @@ plugins {
 }
 
 allprojects {
-    version = "0.3.1"
+    version = "0.3.0"
     group = "de.thetadev.formconductor"
 }
diff --git a/compose-ui/consumer-rules.pro b/compose-ui/consumer-rules.pro
index 2e02e3e..57ccb1e 100644
--- a/compose-ui/consumer-rules.pro
+++ b/compose-ui/consumer-rules.pro
@@ -1,9 +1,7 @@
-# Keep custom validaton rules
--keep class * extends de.thetadev.formconductor.validation.rules.ValidationRule {
-    public static ** INSTANCE;
+-keepclassmembers class * extends de.thetadev.formconductor.validation.rules.ValidationRule {
     <methods>;
     public static <fields>;
-}
+ }
 
 # Keep classes and properties annotated with @Form
 -if @de.thetadev.formconductor.annotations.Form class **
diff --git a/core/src/main/java/de/thetadev/formconductor/validation/rules/OptionalStateRule.kt b/core/src/main/java/de/thetadev/formconductor/validation/rules/OptionalStateRule.kt
index 74dcae7..f91f6b9 100644
--- a/core/src/main/java/de/thetadev/formconductor/validation/rules/OptionalStateRule.kt
+++ b/core/src/main/java/de/thetadev/formconductor/validation/rules/OptionalStateRule.kt
@@ -1,5 +1,5 @@
 package de.thetadev.formconductor.validation.rules
 
-interface OptionalStateRule<T>: ValidationRule {
+interface OptionalStateRule<T> {
     fun isOptional(state: T): Boolean
 }