diff --git a/src/Main/Base/Test/NRefactoryResolverTests.cs b/src/Main/Base/Test/NRefactoryResolverTests.cs
index 968de794f6..072332d71f 100644
--- a/src/Main/Base/Test/NRefactoryResolverTests.cs
+++ b/src/Main/Base/Test/NRefactoryResolverTests.cs
@@ -752,6 +752,26 @@ class TestClass {
 			LocalResolveResult lr = Resolve<LocalResolveResult>(program, "a", 5);
 			Assert.AreEqual("System.Collections.ArrayList", lr.ResolvedType.FullyQualifiedName, "a");
 		}
+		
+		[Test]
+		public void ResolveNamespaceSD2_863()
+		{
+			string program = @"using System;
+namespace A.C { class D {} }
+namespace A.B.C { class D {} }
+namespace A.B {
+	class TestClass {
+		void Test() {
+			
+		}
+	}
+}
+";
+			NamespaceResolveResult nrr = Resolve<NamespaceResolveResult>(program, "C", 7);
+			Assert.AreEqual("A.B.C", nrr.Name, "nrr.Name");
+			TypeResolveResult trr = Resolve<TypeResolveResult>(program, "C.D", 7);
+			Assert.AreEqual("A.B.C.D", trr.ResolvedClass.FullyQualifiedName, "trr.ResolvedClass.FullyQualifiedName");
+		}
 		#endregion
 		
 		#region Import class tests
diff --git a/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/NRefactoryResolver/NRefactoryASTConvertVisitor.cs b/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/NRefactoryResolver/NRefactoryASTConvertVisitor.cs
index 200471627b..bc5dc58608 100644
--- a/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/NRefactoryResolver/NRefactoryASTConvertVisitor.cs
+++ b/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/NRefactoryResolver/NRefactoryASTConvertVisitor.cs
@@ -21,7 +21,7 @@ namespace ICSharpCode.SharpDevelop.Dom.NRefactoryResolver
 	public class NRefactoryASTConvertVisitor : AbstractAstVisitor
 	{
 		ICompilationUnit cu;
-		Stack currentNamespace = new Stack();
+		Stack<string> currentNamespace = new Stack<string>();
 		Stack<DefaultClass> currentClass = new Stack<DefaultClass>();
 		
 		public ICompilationUnit Cu {
@@ -252,7 +252,7 @@ namespace ICSharpCode.SharpDevelop.Dom.NRefactoryResolver
 			if (currentNamespace.Count == 0) {
 				name = namespaceDeclaration.Name;
 			} else {
-				name = (string)currentNamespace.Peek() + '.' + namespaceDeclaration.Name;
+				name = currentNamespace.Peek() + '.' + namespaceDeclaration.Name;
 			}
 			
 			currentNamespace.Push(name);
@@ -300,7 +300,7 @@ namespace ICSharpCode.SharpDevelop.Dom.NRefactoryResolver
 				if (currentNamespace.Count == 0) {
 					c.FullyQualifiedName = typeDeclaration.Name;
 				} else {
-					c.FullyQualifiedName = (string)currentNamespace.Peek() + '.' + typeDeclaration.Name;
+					c.FullyQualifiedName = currentNamespace.Peek() + '.' + typeDeclaration.Name;
 				}
 				cu.Classes.Add(c);
 			}
@@ -403,7 +403,7 @@ namespace ICSharpCode.SharpDevelop.Dom.NRefactoryResolver
 				if (currentNamespace.Count == 0) {
 					c.FullyQualifiedName = name;
 				} else {
-					c.FullyQualifiedName = (string)currentNamespace.Peek() + '.' + name;
+					c.FullyQualifiedName = currentNamespace.Peek() + '.' + name;
 				}
 				cu.Classes.Add(c);
 			}
diff --git a/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/ProjectContent/DefaultProjectContent.cs b/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/ProjectContent/DefaultProjectContent.cs
index 176aeadacb..df7f9e9d82 100644
--- a/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/ProjectContent/DefaultProjectContent.cs
+++ b/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/ProjectContent/DefaultProjectContent.cs
@@ -737,22 +737,19 @@ namespace ICSharpCode.SharpDevelop.Dom
 				}
 			}
 			if (curType != null) {
-				// Try parent namespaces of the current class
+				// Try relative to current namespace and relative to parent namespaces
 				string fullname = curType.Namespace;
-				if (fullname != null && fullname.Length > 0) {
-					string[] namespaces = fullname.Split('.');
-					StringBuilder curnamespace = new StringBuilder();
-					for (int i = 0; i < namespaces.Length; ++i) {
-						curnamespace.Append(namespaces[i]);
-						curnamespace.Append('.');
-						
-						curnamespace.Append(name);
-						string nameSpace = curnamespace.ToString();
-						if (NamespaceExists(nameSpace)) {
-							return nameSpace;
-						}
-						// remove class name again to try next namespace
-						curnamespace.Length -= name.Length;
+				while (fullname != null && fullname.Length > 0) {
+					string nameSpace = fullname + '.' + name;
+					if (NamespaceExists(nameSpace)) {
+						return nameSpace;
+					}
+					
+					int pos = fullname.LastIndexOf('.');
+					if (pos < 0) {
+						fullname = null;
+					} else {
+						fullname = fullname.Substring(0, pos);
 					}
 				}
 			}