diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index bb5527c062..9266558f97 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1,6 +1,6 @@
 <!-- doc/src/sgml/config.sgml -->
 
-<chapter Id="runtime-config">
+<chapter id="runtime-config">
   <title>Server Configuration</title>
 
   <indexterm>
diff --git a/doc/src/sgml/recovery-config.sgml b/doc/src/sgml/recovery-config.sgml
index 7f515dc011..144b880f42 100644
--- a/doc/src/sgml/recovery-config.sgml
+++ b/doc/src/sgml/recovery-config.sgml
@@ -1,6 +1,6 @@
 <!-- doc/src/sgml/recovery-config.sgml -->
 
-<chapter Id="recovery-config">
+<chapter id="recovery-config">
   <title>Recovery Configuration</title>
 
   <indexterm>
diff --git a/doc/src/sgml/typeconv.sgml b/doc/src/sgml/typeconv.sgml
index 71ddc0f30b..f233e9d712 100644
--- a/doc/src/sgml/typeconv.sgml
+++ b/doc/src/sgml/typeconv.sgml
@@ -1,6 +1,6 @@
 <!-- doc/src/sgml/typeconv.sgml -->
 
-<chapter Id="typeconv">
+<chapter id="typeconv">
 <title>Type Conversion</title>
 
 <indexterm zone="typeconv">