diff --git a/docs/generators/adapter.md b/docs/generators/adapter.md
index 7b5980a..1ac242d 100644
--- a/docs/generators/adapter.md
+++ b/docs/generators/adapter.md
@@ -248,6 +248,7 @@ public static partial class Adapters
 | **PKADP015** | Error | Mapping method must be accessible (public or internal) |
 | **PKADP016** | Error | Static members are not supported |
 | **PKADP017** | Error | Ref-return members are not supported |
+| **PKADP018** | Error | Indexers are not supported |
 
 ## Limitations
 
diff --git a/src/PatternKit.Generators/Adapter/AdapterGenerator.cs b/src/PatternKit.Generators/Adapter/AdapterGenerator.cs
index e2565a3..85d8f5f 100644
--- a/src/PatternKit.Generators/Adapter/AdapterGenerator.cs
+++ b/src/PatternKit.Generators/Adapter/AdapterGenerator.cs
@@ -38,6 +38,7 @@ public sealed class AdapterGenerator : IIncrementalGenerator
     private const string DiagIdMappingMethodNotAccessible = "PKADP015";
     private const string DiagIdStaticMembersNotSupported = "PKADP016";
     private const string DiagIdRefReturnNotSupported = "PKADP017";
+    private const string DiagIdIndexersNotSupported = "PKADP018";
 
     private static readonly DiagnosticDescriptor HostNotStaticPartialDescriptor = new(
         id: DiagIdHostNotStaticPartial,
@@ -175,6 +176,14 @@ public sealed class AdapterGenerator : IIncrementalGenerator
         defaultSeverity: DiagnosticSeverity.Error,
         isEnabledByDefault: true);
 
+    private static readonly DiagnosticDescriptor IndexersNotSupportedDescriptor = new(
+        id: DiagIdIndexersNotSupported,
+        title: "Indexers are not supported",
+        messageFormat: "Target type '{0}' contains indexer '{1}' which is not supported by the adapter generator",
+        category: "PatternKit.Generators.Adapter",
+        defaultSeverity: DiagnosticSeverity.Error,
+        isEnabledByDefault: true);
+
     public void Initialize(IncrementalGeneratorInitializationContext context)
     {
         // Find all class declarations with [GenerateAdapter] attribute
@@ -192,11 +201,14 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
 
             var node = typeContext.TargetNode;
 
+            // Track generated adapter type names to detect conflicts (namespace -> type name -> location)
+            var generatedAdapters = new Dictionary<string, Dictionary<string, Location>>();
+
             // Process each [GenerateAdapter] attribute on the host
             foreach (var attr in typeContext.Attributes.Where(a =>
                 a.AttributeClass?.ToDisplayString() == "PatternKit.Generators.Adapter.GenerateAdapterAttribute"))
             {
-                GenerateAdapterForAttribute(spc, hostSymbol, attr, node, typeContext.SemanticModel);
+                GenerateAdapterForAttribute(spc, hostSymbol, attr, node, typeContext.SemanticModel, generatedAdapters);
             }
         });
     }
@@ -206,7 +218,8 @@ private void GenerateAdapterForAttribute(
         INamedTypeSymbol hostSymbol,
         AttributeData attribute,
         SyntaxNode node,
-        SemanticModel semanticModel)
+        SemanticModel semanticModel,
+        Dictionary<string, Dictionary<string, Location>> generatedAdapters)
     {
         // Validate host is static partial
         if (!IsStaticPartial(node))
@@ -277,11 +290,23 @@ private void GenerateAdapterForAttribute(
         if (config.TargetType.TypeKind == TypeKind.Class && config.TargetType.IsAbstract)
         {
             var hasAccessibleParameterlessCtor = config.TargetType.InstanceConstructors
-                .Any(c => c.Parameters.Length == 0 &&
-                         (c.DeclaredAccessibility == Accessibility.Public ||
-                          c.DeclaredAccessibility == Accessibility.Protected ||
-                          c.DeclaredAccessibility == Accessibility.ProtectedOrInternal ||
-                          c.DeclaredAccessibility == Accessibility.Internal));
+                .Any(c =>
+                {
+                    if (c.Parameters.Length > 0)
+                        return false;
+
+                    var accessibility = c.DeclaredAccessibility;
+                    if (accessibility == Accessibility.Public ||
+                        accessibility == Accessibility.Protected ||
+                        accessibility == Accessibility.ProtectedOrInternal)
+                        return true;
+
+                    // Internal constructors are only accessible if in the same assembly
+                    if (accessibility == Accessibility.Internal)
+                        return semanticModel.Compilation.IsSymbolAccessibleWithin(c, semanticModel.Compilation.Assembly);
+
+                    return false;
+                });
 
             if (!hasAccessibleParameterlessCtor)
             {
@@ -396,7 +421,7 @@ private void GenerateAdapterForAttribute(
                 ? string.Empty
                 : hostSymbol.ContainingNamespace.ToDisplayString());
 
-        // Check for type name conflict (PKADP006)
+        // Check for type name conflict (PKADP006) - both in existing compilation and in current generator run
         if (HasTypeNameConflict(semanticModel.Compilation, ns, adapterTypeName))
         {
             context.ReportDiagnostic(Diagnostic.Create(
@@ -407,6 +432,24 @@ private void GenerateAdapterForAttribute(
             return;
         }
 
+        // Check for conflict with adapters being generated in this run
+        var normalizedNs = string.IsNullOrEmpty(ns) ? "" : ns;
+        if (!generatedAdapters.ContainsKey(normalizedNs))
+            generatedAdapters[normalizedNs] = new Dictionary<string, Location>();
+
+        if (generatedAdapters[normalizedNs].ContainsKey(adapterTypeName))
+        {
+            context.ReportDiagnostic(Diagnostic.Create(
+                TypeNameConflictDescriptor,
+                node.GetLocation(),
+                adapterTypeName,
+                string.IsNullOrEmpty(ns) ? "<global>" : ns));
+            return;
+        }
+
+        // Track this adapter type name
+        generatedAdapters[normalizedNs][adapterTypeName] = node.GetLocation();
+
         // Generate adapter
         var source = GenerateAdapterCode(
             adapterTypeName,
@@ -499,6 +542,16 @@ private List<Diagnostic> ValidateTargetMembers(INamedTypeSymbol targetType, Loca
                         evt.Name));
                 }
 
+                // Check for indexers (not supported) - must be checked before other property checks
+                if (member is IPropertySymbol propertySymbol && propertySymbol.IsIndexer)
+                {
+                    diagnostics.Add(Diagnostic.Create(
+                        IndexersNotSupportedDescriptor,
+                        location,
+                        targetType.Name,
+                        propertySymbol.ToDisplayString()));
+                }
+
                 // Check for settable properties (not supported)
                 if (member is IPropertySymbol prop && !prop.IsIndexer && prop.SetMethod is not null)
                 {
@@ -510,7 +563,7 @@ private List<Diagnostic> ValidateTargetMembers(INamedTypeSymbol targetType, Loca
                 }
 
                 // Check for ref-return properties (not supported)
-                if (member is IPropertySymbol refProp && refProp.ReturnsByRef)
+                if (member is IPropertySymbol refProp && !refProp.IsIndexer && refProp.ReturnsByRef)
                 {
                     diagnostics.Add(Diagnostic.Create(
                         RefReturnNotSupportedDescriptor,
diff --git a/src/PatternKit.Generators/AnalyzerReleases.Unshipped.md b/src/PatternKit.Generators/AnalyzerReleases.Unshipped.md
index 947541b..ce3dcad 100644
--- a/src/PatternKit.Generators/AnalyzerReleases.Unshipped.md
+++ b/src/PatternKit.Generators/AnalyzerReleases.Unshipped.md
@@ -115,3 +115,4 @@ PKADP014 | PatternKit.Generators.Adapter | Error | Nested or generic host not su
 PKADP015 | PatternKit.Generators.Adapter | Error | Mapping method must be accessible
 PKADP016 | PatternKit.Generators.Adapter | Error | Static members are not supported
 PKADP017 | PatternKit.Generators.Adapter | Error | Ref-return members are not supported
+PKADP018 | PatternKit.Generators.Adapter | Error | Indexers are not supported