diff --git a/src/doc/user/usermanual.html b/src/doc/user/usermanual.html
index 5c705488..4eec2043 100644
--- a/src/doc/user/usermanual.html
+++ b/src/doc/user/usermanual.html
@@ -5498,6 +5498,14 @@ text/html       [file:///Users/uncrypted-dockes/projets/bateaux/ilur/factEtCie/r
         these will generate phrase queries, which may degrade
         performance and will disable stemming expansion for the
         phrase terms.</p>
+        <p>The contents of the synonyms file must be casefolded
+        (not only lowercased), because this is what expected at the
+        point in the query processing where it is used. There are a
+        few cases where this makes a difference, for example,
+        German sharp s should be expressed as <code class=
+        "literal">ss</code>, Greek final sigma as sigma. For
+        reference, Python3 has an easy way to casefold words
+        (str.casefold()).</p>
         <p>The synonyms file can be specified in the <span class=
         "guilabel">Search parameters</span> tab of the <span class=
         "guilabel">GUI configuration</span> <span class=
@@ -5511,7 +5519,8 @@ text/html       [file:///Users/uncrypted-dockes/projets/bateaux/ilur/factEtCie/r
         synonyms file itself is not subjected to stem expansion.
         This means that a match will not be found if the form
         present in the synonyms file is not present anywhere in the
-        document set.</p>
+        document set (same with accents when using a raw
+        index).</p>
         <p>The synonyms function is probably not going to help you
         find your letters to Mr. Smith. It is best used for
         domain-specific searches. For example, it was initially
diff --git a/src/doc/user/usermanual.xml b/src/doc/user/usermanual.xml
index 88f87dd1..47f69462 100644
--- a/src/doc/user/usermanual.xml
+++ b/src/doc/user/usermanual.xml
@@ -4182,7 +4182,8 @@ text/html       [file:///Users/uncrypted-dockes/projets/bateaux/ilur/factEtCie/r
         containing terms which are synonyms of the ones specified by the user,
         either by expanding the query for all synonyms, or by reducing the user
         entry to canonical terms (the latter only works if the corresponding
-        processing has been performed while creating the index).</para></listitem>
+        processing has been performed while creating the
+        index).</para></listitem> 
       </itemizedlist>
       </para>
       </formalpara>
@@ -4213,6 +4214,13 @@ text/html       [file:///Users/uncrypted-dockes/projets/bateaux/ilur/factEtCie/r
       generate phrase queries, which may degrade performance and will disable
       stemming expansion for the phrase terms.</para>
 
+      <para>The contents of the synonyms file must be casefolded (not only
+      lowercased), because this is what expected at the point in the query
+      processing where it is used. There are a few cases where this makes a
+      difference, for example, German sharp s should be expressed as
+      <literal>ss</literal>, Greek final sigma as sigma. For reference,
+      Python3 has an easy way to casefold words (str.casefold()).</para>
+      
       <para>The synonyms file can be specified in the <guilabel>Search
       parameters</guilabel> tab of the <guilabel>GUI configuration</guilabel>
       <guilabel>Preferences</guilabel> menu entry, or as an option for
@@ -4226,7 +4234,7 @@ text/html       [file:///Users/uncrypted-dockes/projets/bateaux/ilur/factEtCie/r
       latter are stem-expanded, but the contents of the synonyms file itself
       is not subjected to stem expansion. This means that a match will not be
       found if the form present in the synonyms file is not present anywhere
-      in the document set.</para>
+      in the document set (same with accents when using a raw index).</para>
 
       <para>The synonyms function is probably not going to help you find your
       letters to Mr. Smith. It is best used for domain-specific searches. For