diff --git a/src/lexer.py b/src/lexer.py
index 6535aae..2587c91 100644
--- a/src/lexer.py
+++ b/src/lexer.py
@@ -47,7 +47,7 @@ def make_tokens(self):
                     tokens.append(number)
                 else:
                     return [], error
-            elif self.current_char in LETTERS:
+            elif self.current_char in LETTERS + '_':
                 tokens.append(self.make_identifier())
             elif self.current_char == '"' or self.current_char == "'":
                 string_, error = self.make_string(self.current_char)