diff --git a/man/udevadm.xml b/man/udevadm.xml
index 1a9b784776..1a60aef6cf 100644
--- a/man/udevadm.xml
+++ b/man/udevadm.xml
@@ -143,22 +143,25 @@
           <term><option>-x</option></term>
           <term><option>--export</option></term>
           <listitem>
-            <para>Print output as key/value pairs. Values are enclosed in single quotes.</para>
+            <para>Print output as key/value pairs. Values are enclosed in single quotes.
+            This takes effects only when <option>--query=property</option> or
+            <option>--device-id-of-file=<replaceable>FILE</replaceable></option> is specified.</para>
           </listitem>
         </varlistentry>
         <varlistentry>
           <term><option>-P</option></term>
           <term><option>--export-prefix=<replaceable>NAME</replaceable></option></term>
           <listitem>
-            <para>Add a prefix to the key name of exported values.</para>
+            <para>Add a prefix to the key name of exported values.
+            This implies <option>--export</option>.</para>
           </listitem>
         </varlistentry>
         <varlistentry>
           <term><option>-d</option></term>
           <term><option>--device-id-of-file=<replaceable>FILE</replaceable></option></term>
           <listitem>
-            <para>Print major/minor numbers of the underlying device, where the file
-            lives on.</para>
+            <para>Print major/minor numbers of the underlying device, where the file lives on.
+            If this is specified, all positional arguments are ignored.</para>
           </listitem>
         </varlistentry>
         <varlistentry>
diff --git a/src/udev/udevadm-info.c b/src/udev/udevadm-info.c
index ae38e77a83..135a5e0120 100644
--- a/src/udev/udevadm-info.c
+++ b/src/udev/udevadm-info.c
@@ -411,6 +411,7 @@ int info_main(int argc, char *argv[], void *userdata) {
                         arg_export = true;
                         break;
                 case 'P':
+                        arg_export = true;
                         arg_export_prefix = optarg;
                         break;
                 case 'V':