diff --git a/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/MemberLookupHelper.cs b/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/MemberLookupHelper.cs
index e5bcfc5113..46566ff33e 100644
--- a/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/MemberLookupHelper.cs
+++ b/src/Main/ICSharpCode.SharpDevelop.Dom/Project/Src/MemberLookupHelper.cs
@@ -669,6 +669,15 @@ namespace ICSharpCode.SharpDevelop.Dom
 			}
 		}
 		
+		readonly static Dictionary<IReturnType, IEnumerable<IReturnType>> getTypeInheritanceTreeCache = new Dictionary<IReturnType, IEnumerable<IReturnType>>();
+		
+		static void ClearGetTypeInheritanceTreeCache()
+		{
+			lock (getTypeInheritanceTreeCache) {
+				getTypeInheritanceTreeCache.Clear();
+			}
+		}
+		
 		/// <summary>
 		/// Gets all types the specified type inherits from (all classes and interfaces).
 		/// Unlike the class inheritance tree, this method takes care of type arguments and calculates the type
@@ -679,6 +688,12 @@ namespace ICSharpCode.SharpDevelop.Dom
 			if (typeToListInheritanceTreeFor == null)
 				throw new ArgumentNullException("typeToListInheritanceTreeFor");
 			
+			lock (getTypeInheritanceTreeCache) {
+				IEnumerable<IReturnType> result;
+				if (getTypeInheritanceTreeCache.TryGetValue(typeToListInheritanceTreeFor, out result))
+					return result;
+			}
+			
 			IClass classToListInheritanceTreeFor = typeToListInheritanceTreeFor.GetUnderlyingClass();
 			if (classToListInheritanceTreeFor == null)
 				return new IReturnType[] { typeToListInheritanceTreeFor };
@@ -727,6 +742,12 @@ namespace ICSharpCode.SharpDevelop.Dom
 					currentClass = nextType.GetUnderlyingClass();
 				}
 			} while (nextType != null);
+			lock (getTypeInheritanceTreeCache) {
+				if (getTypeInheritanceTreeCache.Count == 0) {
+					DomCache.RegisterForClear(ClearGetTypeInheritanceTreeCache);
+				}
+				getTypeInheritanceTreeCache[typeToListInheritanceTreeFor] = visitedList;
+			}
 			return visitedList;
 		}
 		#endregion