diff --git a/Doc/texinputs/myindex.ist b/Doc/texinputs/myindex.ist
index e12f43e14c4..bfc2e34c8e9 100644
--- a/Doc/texinputs/myindex.ist
+++ b/Doc/texinputs/myindex.ist
@@ -3,7 +3,7 @@ headings_flag 1
 heading_prefix "  \\bigletter "
 
 preamble "\\begin{theindex}
-\\def\\bigletter#1{{\\Large#1}\\vspace{1mm}}
+\\def\\bigletter#1{{\\Large\\sffamily#1}\\vspace{1mm}}
 
 "