1 files changed, 11 insertions, 1 deletions
diff --git a/src/lisp.h b/src/lisp.h
index a34726adbcb..549b51d3f7f 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -2462,7 +2462,7 @@ struct Lisp_Hash_Table
 
   /* Vector of keys and values.  The key of item I is found at index
      2 * I, the value is found at index 2 * I + 1.
-     If the key is equal to Qunbound, then this slot is unused.
+     If the key is HASH_UNUSED_ENTRY_KEY, then this slot is unused.
      This is gc_marked specially if the table is weak.  */
   Lisp_Object key_and_value;
 
@@ -2478,6 +2478,16 @@ struct Lisp_Hash_Table
 /* Sanity-check pseudovector layout.  */
 verify (offsetof (struct Lisp_Hash_Table, weak) == header_size);
 
+/* Key value that marks an unused hash table entry.  */
+#define HASH_UNUSED_ENTRY_KEY Qunbound
+
+/* KEY is a key of an unused hash table entry.  */
+INLINE bool
+hash_unused_entry_key_p (Lisp_Object key)
+{
+  return BASE_EQ (key, HASH_UNUSED_ENTRY_KEY);
+}
+
 INLINE bool
 HASH_TABLE_P (Lisp_Object a)
 {