diff --git a/commons-serialize-generator/src/main/java/io/gitlab/jfronny/commons/serialize/generator/SerializeGeneratorProcessor.java b/commons-serialize-generator/src/main/java/io/gitlab/jfronny/commons/serialize/generator/SerializeGeneratorProcessor.java
index 252a036..9fe1f1e 100644
--- a/commons-serialize-generator/src/main/java/io/gitlab/jfronny/commons/serialize/generator/SerializeGeneratorProcessor.java
+++ b/commons-serialize-generator/src/main/java/io/gitlab/jfronny/commons/serialize/generator/SerializeGeneratorProcessor.java
@@ -115,6 +115,7 @@ public class SerializeGeneratorProcessor extends AbstractProcessor2 {
                                     case "adapter" -> {
                                         if (bld.adapter != null) throw new IllegalArgumentException("Duplicate annotation parameter: adapter");
                                         if (value.getValue() instanceof TypeMirror tm) bld.adapter = tm;
+                                        else if (value.getValue() instanceof String s && s.equals("<error>")) throw new IllegalArgumentException("Unexpected value type on " + element + ". Did you forget to import it?");
                                         else throw new IllegalArgumentException("Unexpected value type: " + value.getValue().getClass() + " (with value " + value.getValue() + ") on " + element);
                                     }
                                     case "nullSafe" -> {