diff --git a/src/xinput.xml b/src/xinput.xml
index e3e71cb..6538726 100644
--- a/src/xinput.xml
+++ b/src/xinput.xml
@@ -395,7 +395,7 @@ authorization from the authors.
     <request name="GrabDeviceButton" opcode="17">
         <field type="WINDOW" name="grab_window" />
         <field type="CARD8"  name="grabbed_device" />
-        <field type="CARD8"  name="modifier_device" />
+        <field type="CARD8"  name="modifier_device" altenum="ModifierDevice" />
         <field type="CARD16" name="num_classes" />
         <field type="CARD16" name="modifiers" mask="ModMask" />
         <field type="CARD8"  name="this_device_mode" enum="GrabMode" />