diff --git a/src/Libraries/NRefactory/Project/Src/Lexer/CSharp/Lexer.cs b/src/Libraries/NRefactory/Project/Src/Lexer/CSharp/Lexer.cs
index 1f59febb21..9ee7a6b8f8 100644
--- a/src/Libraries/NRefactory/Project/Src/Lexer/CSharp/Lexer.cs
+++ b/src/Libraries/NRefactory/Project/Src/Lexer/CSharp/Lexer.cs
@@ -79,7 +79,7 @@ namespace ICSharpCode.NRefactory.Parser.CSharp
 							ch = (char)next;
 							if (ch == '"') {
 								token = ReadVerbatimString();
-							} else if (Char.IsLetterOrDigit(ch)) {
+							} else if (Char.IsLetterOrDigit(ch) || ch == '_') {
 								token = new Token(Tokens.Identifier, x - 1, y, ReadIdent(ch));
 							} else {
 								errors.Error(y, x, String.Format("Unexpected char in Lexer.Next() : {0}", ch));
diff --git a/src/Libraries/NRefactory/Test/Lexer/CSharp/CustomLexerTests.cs b/src/Libraries/NRefactory/Test/Lexer/CSharp/CustomLexerTests.cs
index 386a45dc83..f5864e2db5 100644
--- a/src/Libraries/NRefactory/Test/Lexer/CSharp/CustomLexerTests.cs
+++ b/src/Libraries/NRefactory/Test/Lexer/CSharp/CustomLexerTests.cs
@@ -41,6 +41,34 @@ namespace ICSharpCode.NRefactory.Tests.Lexer.CSharp
 			Assert.AreEqual("a_Bc05", t.val);
 		}
 		
+		[Test]
+		public void TestIdentifierStartingWithUnderscore()
+		{
+			ILexer lexer = GenerateLexer(new StringReader("_Bc05"));
+			Token t = lexer.NextToken();
+			Assert.AreEqual(Tokens.Identifier, t.kind);
+			Assert.AreEqual("_Bc05", t.val);
+		}
+		
+		[Test]
+		public void TestKeyWordAsIdentifier()
+		{
+			ILexer lexer = GenerateLexer(new StringReader("@int"));
+			Token t = lexer.NextToken();
+			Assert.AreEqual(Tokens.Identifier, t.kind);
+			Assert.AreEqual("int", t.val);
+		}
+		
+		
+		[Test]
+		public void TestKeyWordAsIdentifierStartingWithUnderscore()
+		{
+			ILexer lexer = GenerateLexer(new StringReader("@_int"));
+			Token t = lexer.NextToken();
+			Assert.AreEqual(Tokens.Identifier, t.kind);
+			Assert.AreEqual("_int", t.val);
+		}
+		
 		[Test]
 		public void TestSkippedEmptyBlock()
 		{