diff --git a/reference/pgsql/constants.xml b/reference/pgsql/constants.xml
index ef745aa6f9..5df308f9c0 100644
--- a/reference/pgsql/constants.xml
+++ b/reference/pgsql/constants.xml
@@ -5,6 +5,28 @@
  &extension.constants;
  
  <variablelist>
+  <varlistentry xml:id="constant.pgsql-libpq-version">
+   <term>
+    <constant>PGSQL_LIBPQ_VERSION</constant> 
+    (<type>string</type>)
+   </term>
+   <listitem>
+    <simpara>
+     Short libpq version that contains only numbers and dots.
+    </simpara>
+   </listitem>
+  </varlistentry>
+  <varlistentry xml:id="constant.pgsql-libpq-version-str">
+   <term>
+    <constant>PGSQL_LIBPQ_VERSION_STR</constant> 
+    (<type>string</type>)
+   </term>
+   <listitem>
+    <simpara>
+     Long libpq version that includes compiler information.
+    </simpara>
+   </listitem>
+  </varlistentry>
   <varlistentry xml:id="constant.pgsql-assoc">
    <term>
     <constant>PGSQL_ASSOC</constant>