diff --git a/src/Main/Base/Project/ICSharpCode.SharpDevelop.csproj b/src/Main/Base/Project/ICSharpCode.SharpDevelop.csproj
index 6e972e1cb6..c5e8eaf0bc 100644
--- a/src/Main/Base/Project/ICSharpCode.SharpDevelop.csproj
+++ b/src/Main/Base/Project/ICSharpCode.SharpDevelop.csproj
@@ -811,6 +811,7 @@
     <Compile Include="Src\Services\ProjectService\ProjectLoader.cs" />
     <Compile Include="Src\Util\DotnetDetection.cs" />
     <Compile Include="Src\Util\FakeXmlViewContent.cs" />
+    <Compile Include="Src\Util\KeyComparer.cs" />
     <Compile Include="Src\Util\ReactiveExtensions.cs" />
     <Compile Include="Src\Util\TreeNode.cs" />
     <Compile Include="Src\Util\NativeMethods.cs" />
diff --git a/src/Main/Base/Project/Src/Project/MSBuildInternals.cs b/src/Main/Base/Project/Src/Project/MSBuildInternals.cs
index 27446a7aa1..0a97799714 100644
--- a/src/Main/Base/Project/Src/Project/MSBuildInternals.cs
+++ b/src/Main/Base/Project/Src/Project/MSBuildInternals.cs
@@ -7,9 +7,11 @@ using System.Linq;
 using System.Text.RegularExpressions;
 using ICSharpCode.Core;
 using ICSharpCode.SharpDevelop.Dom;
+using ICSharpCode.SharpDevelop.Util;
 using Microsoft.Build.Construction;
 using Microsoft.Build.Execution;
 using Microsoft.Build.Framework;
+using Microsoft.Build.Logging;
 using MSBuild = Microsoft.Build;
 using ProjectCollection = Microsoft.Build.Evaluation.ProjectCollection;
 
@@ -169,6 +171,7 @@ namespace ICSharpCode.SharpDevelop.Project
 		{
 			ProjectInstance project = baseProject.CreateProjectInstance();
 			project.SetProperty("BuildingProject", "false");
+			project.SetProperty("DesignTimeBuild", "true");
 			
 			List<ProjectItemInstance> references = (
 				from item in project.Items
@@ -201,9 +204,16 @@ namespace ICSharpCode.SharpDevelop.Project
 				}
 			}
 			
-			string[] targets = { "ResolveAssemblyReferences" };
-			BuildRequestData requestData = new BuildRequestData(project, targets, new HostServices());
+			List<string> targets = new List<string>();
+			if (baseProject.HasProjectType(ProjectTypeGuids.PortableLibrary)) {
+				targets.Add("ResolveReferences");
+				targets.Add("DesignTimeResolveAssemblyReferences");
+			} else {
+				targets.Add("ResolveAssemblyReferences");
+			}
+			BuildRequestData requestData = new BuildRequestData(project, targets.ToArray(), new HostServices());
 			List<ILogger> loggers = new List<ILogger>();
+			//loggers.Add(new ConsoleLogger(LoggerVerbosity.Diagnostic));
 			if (logErrorsToOutputPad)
 				loggers.Add(new SimpleErrorLogger());
 			lock (SolutionProjectCollectionLock) {
@@ -231,6 +241,8 @@ namespace ICSharpCode.SharpDevelop.Project
 				CopyLocal = bool.Parse(msbuildItem.GetMetadataValue("CopyLocal")),
 				ReferenceItems = referenceItems
 			};
+			// HACK: mscorlib is reported twice for portable library projects (even if we don't specify it as additionalReference)
+			query = query.DistinctBy(asm => asm.FullPath);
 			List<ReferenceProjectItem> resolvedAssemblies = new List<ReferenceProjectItem>();
 			List<ReferenceProjectItem> handledReferenceItems = new List<ReferenceProjectItem>();
 			foreach (var assembly in query) {
diff --git a/src/Main/Base/Project/Src/Util/ExtensionMethods.cs b/src/Main/Base/Project/Src/Util/ExtensionMethods.cs
index 690537f4c1..e759706bab 100644
--- a/src/Main/Base/Project/Src/Util/ExtensionMethods.cs
+++ b/src/Main/Base/Project/Src/Util/ExtensionMethods.cs
@@ -22,6 +22,7 @@ using ICSharpCode.NRefactory;
 using ICSharpCode.SharpDevelop.Dom;
 using ICSharpCode.SharpDevelop.Editor;
 using ICSharpCode.SharpDevelop.Gui;
+using ICSharpCode.SharpDevelop.Util;
 using WinForms = System.Windows.Forms;
 
 namespace ICSharpCode.SharpDevelop
@@ -160,6 +161,11 @@ namespace ICSharpCode.SharpDevelop
 			return result;
 		}
 		
+		public static IEnumerable<T> DistinctBy<T, K>(this IEnumerable<T> input, Func<T, K> keySelector)
+		{
+			return input.Distinct(KeyComparer.Create(keySelector));
+		}
+		
 		/// <summary>
 		/// Sets the Content property of the specified ControlControl to the specified content.
 		/// If the content is a Windows-Forms control, it is wrapped in a WindowsFormsHost.
diff --git a/src/Main/Base/Project/Src/Util/KeyComparer.cs b/src/Main/Base/Project/Src/Util/KeyComparer.cs
new file mode 100644
index 0000000000..4a8cce5b46
--- /dev/null
+++ b/src/Main/Base/Project/Src/Util/KeyComparer.cs
@@ -0,0 +1,45 @@
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
+// This code is distributed under the GNU LGPL (for details please see \doc\license.txt)
+
+using System;
+using System.Collections.Generic;
+
+namespace ICSharpCode.SharpDevelop.Util
+{
+	public static class KeyComparer
+	{
+		public static KeyComparer<TElement, TKey> Create<TElement, TKey>(Func<TElement, TKey> keySelector)
+		{
+			return new KeyComparer<TElement, TKey>(keySelector, Comparer<TKey>.Default, EqualityComparer<TKey>.Default);
+		}
+	}
+	
+	public class KeyComparer<TElement, TKey> : IComparer<TElement>, IEqualityComparer<TElement>
+	{
+		readonly Func<TElement, TKey> keySelector;
+		readonly IComparer<TKey> keyComparer;
+		readonly IEqualityComparer<TKey> keyEqualityComparer;
+		
+		public KeyComparer(Func<TElement, TKey> keySelector, IComparer<TKey> keyComparer, IEqualityComparer<TKey> keyEqualityComparer)
+		{
+			this.keySelector = keySelector;
+			this.keyComparer = keyComparer;
+			this.keyEqualityComparer = keyEqualityComparer;
+		}
+		
+		public int Compare(TElement x, TElement y)
+		{
+			return keyComparer.Compare(keySelector(x), keySelector(y));
+		}
+		
+		public bool Equals(TElement x, TElement y)
+		{
+			return keyEqualityComparer.Equals(keySelector(x), keySelector(y));
+		}
+		
+		public int GetHashCode(TElement obj)
+		{
+			return keyEqualityComparer.GetHashCode(keySelector(obj));
+		}
+	}
+}