diff --git a/src/runtime/subtree.h b/src/runtime/subtree.h
index 04aa5347..31c942e0 100644
--- a/src/runtime/subtree.h
+++ b/src/runtime/subtree.h
@@ -17,16 +17,13 @@ extern TSStateId TS_TREE_STATE_NONE;
 typedef struct {
   union {
     char *long_data;
-    char short_data[sizeof(char *) + sizeof(uint32_t)];
+    char short_data[16];
   };
   uint32_t length;
 } ExternalScannerState;
 
 typedef struct Subtree Subtree;
 
-typedef Array(const Subtree *) SubtreeArray;
-typedef Array(Subtree *) MutableSubtreeArray;
-
 struct Subtree {
   Length padding;
   Length size;
@@ -71,6 +68,9 @@ struct Subtree {
   };
 };
 
+typedef Array(const Subtree *) SubtreeArray;
+typedef Array(Subtree *) MutableSubtreeArray;
+
 typedef struct {
   MutableSubtreeArray free_trees;
   MutableSubtreeArray tree_stack;