diff --git a/ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/ValueParameterUnusedIssue.cs b/ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/ValueParameterUnusedIssue.cs
index 6381c7b5b2..845b5341f2 100644
--- a/ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/ValueParameterUnusedIssue.cs
+++ b/ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/ValueParameterUnusedIssue.cs
@@ -66,8 +66,8 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 				// don't warn on empty custom events
 				if (addAccessor.Body.Statements.Count == 0 && removeAccessor.Body.Statements.Count == 0)
 					return;
-				FindIssuesInNode(addAccessor, addAccessor.Body, "add accessor");
-				FindIssuesInNode(removeAccessor, removeAccessor.Body, "remove accessor");
+				FindIssuesInAccessor(addAccessor, "add accessor");
+				FindIssuesInAccessor(removeAccessor, "remove accessor");
 			}
 
 			void FindIssuesInAccessor(Accessor accessor, string accessorName = "setter")
diff --git a/ICSharpCode.NRefactory.Tests/TypeSystem/TypeSystemTests.cs b/ICSharpCode.NRefactory.Tests/TypeSystem/TypeSystemTests.cs
index 2b49e45733..8ac4628b2c 100644
--- a/ICSharpCode.NRefactory.Tests/TypeSystem/TypeSystemTests.cs
+++ b/ICSharpCode.NRefactory.Tests/TypeSystem/TypeSystemTests.cs
@@ -73,6 +73,7 @@ namespace ICSharpCode.NRefactory.TypeSystem
 			Assert.AreEqual(0, method.Parameters.Count);
 			Assert.AreEqual(0, method.Attributes.Count);
 			Assert.IsTrue(method.HasBody);
+			Assert.IsNull(method.AccessorOwner);
 		}
 		
 		[Test]
@@ -246,6 +247,14 @@ namespace ICSharpCode.NRefactory.TypeSystem
 			Assert.AreEqual(m12, m2);
 		}
 		
+		[Test]
+		public void SpecializedMethod_AccessorOwner()
+		{
+			// NRefactory bug #143 - Accessor Owner throws null reference exception in some cases now
+			var method = compilation.FindType(typeof(GenericClass<string, object>)).GetMethods(m => m.Name == "GetIndex").Single();
+			Assert.IsNull(method.AccessorOwner);
+		}
+		
 		[Test]
 		public void Specialized_GetIndex_ToMemberReference()
 		{
diff --git a/ICSharpCode.NRefactory/TypeSystem/Implementation/SpecializedMethod.cs b/ICSharpCode.NRefactory/TypeSystem/Implementation/SpecializedMethod.cs
index ca5eee49f2..0721c95362 100644
--- a/ICSharpCode.NRefactory/TypeSystem/Implementation/SpecializedMethod.cs
+++ b/ICSharpCode.NRefactory/TypeSystem/Implementation/SpecializedMethod.cs
@@ -142,7 +142,10 @@ namespace ICSharpCode.NRefactory.TypeSystem.Implementation
 				if (result != null) {
 					return result;
 				} else {
-					result = methodDefinition.AccessorOwner.Specialize(this.Substitution);
+					var ownerDefinition = methodDefinition.AccessorOwner;
+					if (ownerDefinition == null)
+						return null;
+					result = ownerDefinition.Specialize(this.Substitution);
 					return LazyInit.GetOrSet(ref accessorOwner, result);
 				}
 			}