diff --git a/doc/flatpak-metadata.xml b/doc/flatpak-metadata.xml
index 97f789067..c8544391d 100644
--- a/doc/flatpak-metadata.xml
+++ b/doc/flatpak-metadata.xml
@@ -499,7 +499,7 @@
                 <varlistentry>
                     <term><option>build</option> (boolean)</term>
                     <listitem><para>
-                        Whether this instance was created by flatpak build. 
+                        Whether this instance was created by flatpak build.
                     </para></listitem>
                 </varlistentry>
                 <varlistentry>
@@ -805,6 +805,15 @@
                         belongs to. Available since 0.9.1.
                     </para></listitem>
                 </varlistentry>
+                <varlistentry>
+                    <term><option>runtime</option> (string)</term>
+                    <listitem><para>
+                        The runtime this extension will be inside of. If it is an
+                        app extension, this is the app's runtime; otherwise, this
+                        is identical to ref, without the runtime/ prefix.
+                        Available since 1.5.0.
+                    </para></listitem>
+                </varlistentry>
                 <varlistentry>
                     <term><option>priority</option> (integer)</term>
                     <listitem><para>