diff --git a/nml/tokens.py b/nml/tokens.py
index 2591feaf..821e2dd2 100644
--- a/nml/tokens.py
+++ b/nml/tokens.py
@@ -195,7 +195,7 @@ def t_ignore_comment(self, t):
         self.increment_lines(t.value.count("\n"))
 
     def t_ignore_whitespace(self, t):
-        "[ \t\r]+"
+        r"[ \t\r]+"
         pass
 
     def t_line_directive1(self, t):