diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index c60d98360f..0b5571460d 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -26256,7 +26256,8 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
        </para>
        <para>
         Shows the compression algorithm that was used to compress a
-        an individual variable-length value.
+        an individual variable-length value. Returns <literal>NULL</literal>
+        if the value is not compressed.
        </para></entry>
       </row>
 
diff --git a/doc/src/sgml/ref/alter_materialized_view.sgml b/doc/src/sgml/ref/alter_materialized_view.sgml
index 27f60f6df5..7011a0e7da 100644
--- a/doc/src/sgml/ref/alter_materialized_view.sgml
+++ b/doc/src/sgml/ref/alter_materialized_view.sgml
@@ -40,6 +40,7 @@ ALTER MATERIALIZED VIEW ALL IN TABLESPACE <replaceable class="parameter">name</r
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET ( <replaceable class="parameter">attribute_option</replaceable> = <replaceable class="parameter">value</replaceable> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> RESET ( <replaceable class="parameter">attribute_option</replaceable> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
+    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET COMPRESSION <replaceable class="parameter">compression_method</replaceable>
     CLUSTER ON <replaceable class="parameter">index_name</replaceable>
     SET WITHOUT CLUSTER
     SET ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] )