diff --git a/ChangeLog b/ChangeLog
index c382d58..2f32364 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2010-02-14  Colin Watson  <address@hidden>
+
+	* lib/hash.c (hash_contains): New function (trivial modification of
+	hash_lookup).
+	* lib/hash.h (hash_contains): New declaration.
+	* tests/test-hash.c (main): Test hash_contains.
+
 2010-02-10  Jim Meyering  <address@hidden>
 
 	maint.mk: prohibit inclusion of "ignore-value.h" without_use
diff --git a/lib/hash.c b/lib/hash.c
index f9abb9f..de8b778 100644
--- a/lib/hash.c
+++ b/lib/hash.c
@@ -243,6 +243,28 @@ hash_print_statistics (const Hash_table *table, FILE *stream)
            (unsigned long int) max_bucket_length);
 }
 
+/* Return true if ENTRY matches an entry already in the hash table.  */
+
+bool
+hash_contains (const Hash_table *table, const void *entry)
+{
+  struct hash_entry const *bucket
+    = table->bucket + table->hasher (entry, table->n_buckets);
+  struct hash_entry const *cursor;
+
+  if (! (bucket < table->bucket_limit))
+    abort ();
+
+  if (bucket->data == NULL)
+    return false;
+
+  for (cursor = bucket; cursor; cursor = cursor->next)
+    if (entry == cursor->data || table->comparator (entry, cursor->data))
+      return true;
+
+  return false;
+}
+
 /* If ENTRY matches an entry already in the hash table, return the
    entry from the table.  Otherwise, return NULL.  */
 
diff --git a/lib/hash.h b/lib/hash.h
index e795cdc..00e2e1a 100644
--- a/lib/hash.h
+++ b/lib/hash.h
@@ -68,6 +68,7 @@ size_t hash_get_n_entries (const Hash_table *);
 size_t hash_get_max_bucket_length (const Hash_table *);
 bool hash_table_ok (const Hash_table *);
 void hash_print_statistics (const Hash_table *, FILE *);
+bool hash_contains (const Hash_table *, const void *);
 void *hash_lookup (const Hash_table *, const void *);
 
 /* Walking.  */
diff --git a/tests/test-hash.c b/tests/test-hash.c
index 1715033..756f0ae 100644
--- a/tests/test-hash.c
+++ b/tests/test-hash.c
@@ -164,7 +164,9 @@ main (int argc, char **argv)
         char *str = xstrdup ("a");
         insert_new (ht, "a");
         insert_new (ht, str);
+        ASSERT (hash_contains (ht, str));
         ASSERT (hash_lookup (ht, str) == str);
+        ASSERT (!hash_contains (ht, "b"));
         free (str);
       }
       hash_free (ht);