diff --git a/src/Libraries/NRefactory/Project/Src/Lexer/AbstractLexer.cs b/src/Libraries/NRefactory/Project/Src/Lexer/AbstractLexer.cs
index c2e76dfffc..805d81dd9b 100644
--- a/src/Libraries/NRefactory/Project/Src/Lexer/AbstractLexer.cs
+++ b/src/Libraries/NRefactory/Project/Src/Lexer/AbstractLexer.cs
@@ -46,6 +46,21 @@ namespace ICSharpCode.NRefactory.Parser
 			get { throw new NotSupportedException(); }
 		}
 		
+		protected static IEnumerable<string> GetSymbols (string symbols)
+		{
+			foreach (string symbol in symbols.Split (';')) {
+				string s = symbol.Trim ();
+				if (s.Length == 0)
+					continue;
+				yield return s;
+			}
+		}
+		
+		public virtual void SetConditionalCompilationSymbols (string symbols)
+		{
+			throw new NotSupportedException ();
+		}
+		
 		protected int Line {
 			get {
 				return line;
diff --git a/src/Libraries/NRefactory/Project/Src/Lexer/CSharp/Lexer.cs b/src/Libraries/NRefactory/Project/Src/Lexer/CSharp/Lexer.cs
index 63a85342d3..02c2d8af17 100644
--- a/src/Libraries/NRefactory/Project/Src/Lexer/CSharp/Lexer.cs
+++ b/src/Libraries/NRefactory/Project/Src/Lexer/CSharp/Lexer.cs
@@ -990,6 +990,14 @@ namespace ICSharpCode.NRefactory.Parser.CSharp
 			get { return conditionalCompilation.Symbols; }
 		}
 		
+		public override void SetConditionalCompilationSymbols (string symbols)
+		{
+			foreach (string symbol in GetSymbols (symbols)) {
+				conditionalCompilation.Define (symbol);
+			}
+		}
+		
+		
 		ConditionalCompilation conditionalCompilation = new ConditionalCompilation();
 		
 		void ReadPreProcessingDirective()
diff --git a/src/Libraries/NRefactory/Project/Src/Lexer/ILexer.cs b/src/Libraries/NRefactory/Project/Src/Lexer/ILexer.cs
index ab647b75f6..26d4f9605d 100644
--- a/src/Libraries/NRefactory/Project/Src/Lexer/ILexer.cs
+++ b/src/Libraries/NRefactory/Project/Src/Lexer/ILexer.cs
@@ -61,6 +61,14 @@ namespace ICSharpCode.NRefactory.Parser
 		/// </summary>
 		IDictionary<string, object> ConditionalCompilationSymbols { get; }
 		
+		/// <summary>
+		/// Sets the conditional compilation symbols. 
+		/// </summary>
+		/// <param name="symbols">
+		/// A <see cref="System.String"/> containing the symbols. The symbols are separated by ';'.
+		/// </param>
+		void SetConditionalCompilationSymbols (string symbols);
+		
 		/// <summary>
 		/// Returns the comments that had been read and containing tag key words.
 		/// </summary>