diff --git a/doc/utils/sphinx-config/LAMMPSLexer.py b/doc/utils/sphinx-config/LAMMPSLexer.py
index a7ba5d92a8..ee548dc602 100644
--- a/doc/utils/sphinx-config/LAMMPSLexer.py
+++ b/doc/utils/sphinx-config/LAMMPSLexer.py
@@ -76,12 +76,12 @@ class LAMMPSLexer(RegexLexer):
             include('conditionals'),
             include('keywords'),
             (r'#.*?\n', Comment),
-            ('"', String, 'string'),
-            ('\'', String, 'single_quote_string'),
+            (r'"', String, 'string'),
+            (r'\'', String, 'single_quote_string'),
             (r'[0-9]+:[0-9]+(:[0-9]+)?', Number),
             (r'[0-9]+(\.[0-9]+)?([eE]\-?[0-9]+)?', Number),
-            ('\$?\(', Name.Variable, 'expression'),
-            ('\$\{', Name.Variable, 'variable'),
+            (r'\$?\(', Name.Variable, 'expression'),
+            (r'\$\{', Name.Variable, 'variable'),
             (r'[\w_\.\[\]]+', Name),
             (r'\$[\w_]+', Name.Variable),
             (r'\s+', Whitespace),
@@ -97,21 +97,21 @@ class LAMMPSLexer(RegexLexer):
         ]
         ,
         'variable' : [
-            ('[^\}]+', Name.Variable),
-            ('\}', Name.Variable, '#pop'),
+            (r'[^\}]+', Name.Variable),
+            (r'\}', Name.Variable, '#pop'),
         ],
         'string' : [
-            ('[^"]+', String),
-            ('"', String, '#pop'),
+            (r'[^"]+', String),
+            (r'"', String, '#pop'),
         ],
         'single_quote_string' : [
-            ('[^\']+', String),
-            ('\'', String, '#pop'),
+            (r'[^\']+', String),
+            (r'\'', String, '#pop'),
         ],
         'expression' : [
-            ('[^\(\)]+', Name.Variable),
-            ('\(', Name.Variable, 'expression'),
-            ('\)', Name.Variable, '#pop'),
+            (r'[^\(\)]+', Name.Variable),
+            (r'\(', Name.Variable, 'expression'),
+            (r'\)', Name.Variable, '#pop'),
         ],
         'modify_cmd' : [
             (r'[\w_\-\.\[\]]+', Name.Variable.Identifier),