diff --git a/Upsilon/Parser/Lexer.cs b/Upsilon/Parser/Lexer.cs
index d8b62d0..c2edbd6 100644
--- a/Upsilon/Parser/Lexer.cs
+++ b/Upsilon/Parser/Lexer.cs
@@ -95,7 +95,7 @@ namespace Upsilon.Parser
                     }
                     return new SyntaxToken(SyntaxKind.Tilde, _position, "~", null);
                 default:
-                    if (char.IsLetter(Current))
+                    if (char.IsLetter(Current) || Current == '_')
                         return LexIdentifierOrKeyword();
                     _diagnostics.LogBadCharacter(new TextSpan(_position, 1), SyntaxKind.Identifier);
                     return new SyntaxToken(SyntaxKind.BadToken, _position, "", null);