diff --git a/common/src/main/java/dev/cel/common/types/UnspecifiedType.java b/common/src/main/java/dev/cel/common/types/UnspecifiedType.java
index 0daf90865..2c1df422e 100644
--- a/common/src/main/java/dev/cel/common/types/UnspecifiedType.java
+++ b/common/src/main/java/dev/cel/common/types/UnspecifiedType.java
@@ -32,7 +32,7 @@
 @CheckReturnValue
 @Immutable
 @Internal
-public class UnspecifiedType extends CelType {
+public abstract class UnspecifiedType extends CelType {
 
   @Override
   public CelKind kind() {