diff --git a/Doc/lib/libzlib.tex b/Doc/lib/libzlib.tex
index d8ecc98045a5..2e76900b6aa9 100644
--- a/Doc/lib/libzlib.tex
+++ b/Doc/lib/libzlib.tex
@@ -51,6 +51,7 @@ exception if any error occurs.
 \begin{funcdesc}{crc32}{string\optional{, value}}
   Computes a CRC (Cyclic Redundancy Check)%
   \index{Cyclic Redundancy Check}
+  \index{checksum!Cyclic Redundancy Check}
   checksum of \var{string}. If
   \var{value} is present, it is used as the starting value of the
   checksum; otherwise, a fixed default value is used.  This allows
diff --git a/Doc/libzlib.tex b/Doc/libzlib.tex
index d8ecc98045a5..2e76900b6aa9 100644
--- a/Doc/libzlib.tex
+++ b/Doc/libzlib.tex
@@ -51,6 +51,7 @@ exception if any error occurs.
 \begin{funcdesc}{crc32}{string\optional{, value}}
   Computes a CRC (Cyclic Redundancy Check)%
   \index{Cyclic Redundancy Check}
+  \index{checksum!Cyclic Redundancy Check}
   checksum of \var{string}. If
   \var{value} is present, it is used as the starting value of the
   checksum; otherwise, a fixed default value is used.  This allows