diff --git a/lib/index.js b/lib/index.js
index 1930f57..a456828 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -31,7 +31,13 @@ function enterFootnoteCallString() {
  * @type {FromMarkdownHandle}
  */
 function enterFootnoteCall(token) {
-  this.enter({type: 'footnoteReference', identifier: '', label: ''}, token)
+  // Trailing `position: undefined` keeps the footnoteReference hidden class
+  // stable; mdast-util-from-markdown's enter() patches the field to a real
+  // value but the property already exists, so no shape transition fires.
+  this.enter(
+    {type: 'footnoteReference', identifier: '', label: '', position: undefined},
+    token
+  )
 }
 
 /**
@@ -47,8 +53,16 @@ function enterFootnoteDefinitionLabelString() {
  * @type {FromMarkdownHandle}
  */
 function enterFootnoteDefinition(token) {
+  // See enterFootnoteCall above for the rationale on the trailing
+  // position field.
   this.enter(
-    {type: 'footnoteDefinition', identifier: '', label: '', children: []},
+    {
+      type: 'footnoteDefinition',
+      identifier: '',
+      label: '',
+      children: [],
+      position: undefined
+    },
     token
   )
 }