diff --git a/sphinx/texinputs/sphinxlatexstyletext.sty b/sphinx/texinputs/sphinxlatexstyletext.sty
index 675eb117847..ab50aed569b 100644
--- a/sphinx/texinputs/sphinxlatexstyletext.sty
+++ b/sphinx/texinputs/sphinxlatexstyletext.sty
@@ -28,8 +28,8 @@
 \def\sphinxstyleindexextra   #1{ (\emph{#1})}
 \def\sphinxstyleindexpageref #1{, \pageref{#1}}
 \def\sphinxstyleindexpagemain#1{\textbf{#1}}
-\protected\def\spxentry#1{#1}% will get \let to \sphinxstyleindexentry in index
-\protected\def\spxextra#1{#1}% will get \let to \sphinxstyleindexextra in index
+\def\spxentry{\@backslashchar spxentry}% let to \sphinxstyleindexentry in index
+\def\spxextra{\@backslashchar spxextra}% let to \sphinxstyleindexextra in index
 \def\sphinxstyleindexlettergroup #1%
     {{\Large\sffamily#1}\nopagebreak\vspace{1mm}}
 \def\sphinxstyleindexlettergroupDefault #1%