diff --git a/test/PatternKit.Generators.Tests/InterpreterGeneratorTests.cs b/test/PatternKit.Generators.Tests/InterpreterGeneratorTests.cs
index 64e55000..ab1ce50a 100644
--- a/test/PatternKit.Generators.Tests/InterpreterGeneratorTests.cs
+++ b/test/PatternKit.Generators.Tests/InterpreterGeneratorTests.cs
@@ -114,6 +114,48 @@ public static partial class PricingRules
         ScenarioExpect.Equal("PKINT003", diagnostic.Id);
     }
 
+    [Scenario("Reports diagnostics for invalid interpreter rule shapes")]
+    [Fact]
+    public void ReportsDiagnosticsForInvalidInterpreterRuleShapes()
+    {
+        var source = """
+            using PatternKit.Generators.Interpreter;
+
+            namespace Demo;
+
+            public sealed class PricingContext;
+
+            [GenerateInterpreter(typeof(PricingContext), typeof(decimal))]
+            public static partial class PricingRules
+            {
+                [InterpreterTerminal(" ")]
+                private static decimal BlankName(string token) => 0m;
+
+                [InterpreterTerminal("void")]
+                private static void VoidTerminal(string token) { }
+
+                [InterpreterTerminal("generic")]
+                private static decimal GenericTerminal<T>(string token) => 0m;
+
+                [InterpreterTerminal("missing-parameter")]
+                private static decimal MissingParameter() => 0m;
+
+                [InterpreterNonTerminal("wrong-first")]
+                private static decimal WrongFirst(string token) => 0m;
+
+                [InterpreterTerminal("wrong-context")]
+                private static decimal WrongContext(string token, object context) => 0m;
+            }
+            """;
+
+        var comp = CreateCompilation(source, nameof(ReportsDiagnosticsForInvalidInterpreterRuleShapes));
+        var gen = new InterpreterGenerator();
+        _ = RoslynTestHelpers.Run(comp, gen, out var run, out _);
+
+        var diagnostics = run.Results.SelectMany(result => result.Diagnostics).ToArray();
+        ScenarioExpect.Equal(6, diagnostics.Count(diagnostic => diagnostic.Id == "PKINT003"));
+    }
+
     [Scenario("Reports diagnostic for duplicate interpreter rules")]
     [Fact]
     public void ReportsDiagnosticForDuplicateInterpreterRules()
diff --git a/test/PatternKit.Generators.Tests/ObserverGeneratorTests.cs b/test/PatternKit.Generators.Tests/ObserverGeneratorTests.cs
index c7788d3c..fde50b4f 100644
--- a/test/PatternKit.Generators.Tests/ObserverGeneratorTests.cs
+++ b/test/PatternKit.Generators.Tests/ObserverGeneratorTests.cs
@@ -1070,4 +1070,50 @@ internal partial record class DomainEvent
         var emit = updated.Emit(Stream.Null);
         ScenarioExpect.True(emit.Success, string.Join("\n", emit.Diagnostics));
     }
+
+    [Scenario("Invalid enum configuration falls back to observer defaults")]
+    [Fact]
+    public void Invalid_Enum_Configuration_Falls_Back_To_Observer_Defaults()
+    {
+        const string code = """
+            using PatternKit.Generators.Observer;
+
+            namespace Test;
+
+            public record Payload(int Value);
+
+            [Observer(
+                typeof(Payload),
+                Threading = (ObserverThreadingPolicy)99,
+                Exceptions = (ObserverExceptionPolicy)99,
+                Order = (ObserverOrderPolicy)99)]
+            internal partial class DomainEvent
+            {
+            }
+            """;
+
+        var comp = RoslynTestHelpers.CreateCompilation(
+            code,
+            assemblyName: nameof(Invalid_Enum_Configuration_Falls_Back_To_Observer_Defaults));
+
+        var gen = new Observer.ObserverGenerator();
+        _ = RoslynTestHelpers.Run(comp, gen, out var run, out var updated);
+
+        ScenarioExpect.All(run.Results, r => ScenarioExpect.Empty(r.Diagnostics));
+
+        var generated = run.Results
+            .SelectMany(r => r.GeneratedSources)
+            .Single()
+            .SourceText.ToString();
+
+        ScenarioExpect.Contains("namespace Test;", generated);
+        ScenarioExpect.Contains("internal partial class DomainEvent", generated);
+        ScenarioExpect.Contains("public readonly object Lock = new();", generated);
+        ScenarioExpect.Contains("lock (_state.Lock)", generated);
+        ScenarioExpect.Contains("OnSubscriberError(ex);", generated);
+        ScenarioExpect.DoesNotContain("System.AggregateException", generated);
+
+        var emit = updated.Emit(Stream.Null);
+        ScenarioExpect.True(emit.Success, string.Join("\n", emit.Diagnostics));
+    }
 }