diff --git a/PyTeX/format/constants.py b/PyTeX/format/constants.py
index 331aac2..78d55f9 100644
--- a/PyTeX/format/constants.py
+++ b/PyTeX/format/constants.py
@@ -62,7 +62,7 @@ INS_FILE = [
 
 DRV_FILE = [
     r'\documentclass{{{documentclass}}}',
-    r'{{preamble}}',
+    r'{preamble}',
     r'\begin{{document}}',
     r'\DocInput{{{infile}}}',
     r'\end{{document}}'
diff --git a/PyTeX/format/macros.py b/PyTeX/format/macros.py
index be6ea35..2194a9a 100644
--- a/PyTeX/format/macros.py
+++ b/PyTeX/format/macros.py
@@ -169,7 +169,7 @@ class SimpleSingleLineMacro(SingleLineMacro, ABC):
 
 class GuardMacro(RegexSingleLineMacro):
     def __init__(self):
-        super(GuardMacro, self).__init__(r'<(\*|/|@@=)[a-zA-Z]*>')
+        super(GuardMacro, self).__init__(r'<(\*|/|@@=)[a-zA-Z_]*>')
 
     def _apply(self, line, formatter) -> Union[str, List[str]]:
         match = re.search(self.regex, line)