diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml
index 59664e8891f..b1727b9807a 100644
--- a/doc/src/sgml/ref/select.sgml
+++ b/doc/src/sgml/ref/select.sgml
@@ -704,8 +704,8 @@ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceabl
     The <replaceable class="parameter">frame_clause</> can be one of
 
 <synopsis>
-[ RANGE | ROWS ] <replaceable>frame_start</>
-[ RANGE | ROWS ] BETWEEN <replaceable>frame_start</> AND <replaceable>frame_end</>
+{ RANGE | ROWS } <replaceable>frame_start</>
+{ RANGE | ROWS } BETWEEN <replaceable>frame_start</> AND <replaceable>frame_end</>
 </synopsis>
 
     where <replaceable>frame_start</> and <replaceable>frame_end</> can be
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index 2e5104526a8..1dfb38eec31 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -1725,8 +1725,8 @@ SELECT string_agg(a ORDER BY a, ',') FROM table;  -- incorrect
     and the optional <replaceable class="parameter">frame_clause</replaceable>
     can be one of
 <synopsis>
-[ RANGE | ROWS ] <replaceable>frame_start</>
-[ RANGE | ROWS ] BETWEEN <replaceable>frame_start</> AND <replaceable>frame_end</>
+{ RANGE | ROWS } <replaceable>frame_start</>
+{ RANGE | ROWS } BETWEEN <replaceable>frame_start</> AND <replaceable>frame_end</>
 </synopsis>
     where <replaceable>frame_start</> and <replaceable>frame_end</> can be
     one of