diff --git a/loose.c b/loose.c
index 07333be696..f7a3dd1a72 100644
--- a/loose.c
+++ b/loose.c
@@ -57,7 +57,7 @@ static int insert_loose_map(struct odb_source *source,
 	inserted |= insert_oid_pair(map->to_compat, oid, compat_oid);
 	inserted |= insert_oid_pair(map->to_storage, compat_oid, oid);
 	if (inserted)
-		oidtree_insert(files->loose->cache, compat_oid);
+		oidtree_insert(files->loose->cache, compat_oid, NULL);
 
 	return inserted;
 }
diff --git a/object-file.c b/object-file.c
index 7b1a12f8eb..8705251e4d 100644
--- a/object-file.c
+++ b/object-file.c
@@ -1858,6 +1858,7 @@ static int for_each_object_wrapper_cb(const struct object_id *oid,
 }
 
 static int for_each_prefixed_object_wrapper_cb(const struct object_id *oid,
+					       void *node_data UNUSED,
 					       void *cb_data)
 {
 	struct for_each_object_wrapper_data *data = cb_data;
@@ -2003,7 +2004,7 @@ static int append_loose_object(const struct object_id *oid,
 			       const char *path UNUSED,
 			       void *data)
 {
-	oidtree_insert(data, oid);
+	oidtree_insert(data, oid, NULL);
 	return 0;
 }
 
diff --git a/oidtree.c b/oidtree.c
index 117649753f..e43f18026e 100644
--- a/oidtree.c
+++ b/oidtree.c
@@ -9,6 +9,7 @@
 struct oidtree_node {
 	struct cb_node base;
 	struct object_id key;
+	void *data;
 };
 
 void oidtree_init(struct oidtree *ot)
@@ -25,15 +26,22 @@ void oidtree_clear(struct oidtree *ot)
 	}
 }
 
-void oidtree_insert(struct oidtree *ot, const struct object_id *oid)
+struct oidtree_data {
+	struct object_id oid;
+};
+
+void oidtree_insert(struct oidtree *ot, const struct object_id *oid,
+		    void *data)
 {
 	struct oidtree_node *on;
+	struct cb_node *node;
 
 	if (!oid->algo)
 		BUG("oidtree_insert requires oid->algo");
 
 	on = mem_pool_alloc(&ot->mem_pool, sizeof(*on));
 	oidcpy(&on->key, oid);
+	on->data = data;
 
 	/*
 	 * n.b. Current callers won't get us duplicates, here.  If a
@@ -41,13 +49,19 @@ void oidtree_insert(struct oidtree *ot, const struct object_id *oid)
 	 * that won't be freed until oidtree_clear.  Currently it's not
 	 * worth maintaining a free list
 	 */
-	cb_insert(&ot->tree, &on->base, sizeof(*oid));
+	node = cb_insert(&ot->tree, &on->base, sizeof(*oid));
+	if (node) {
+		struct oidtree_node *preexisting = container_of(node, struct oidtree_node, base);
+		preexisting->data = data;
+	}
 }
 
-bool oidtree_contains(struct oidtree *ot, const struct object_id *oid)
+static struct oidtree_node *oidtree_lookup(struct oidtree *ot,
+					   const struct object_id *oid)
 {
 	struct object_id k;
 	size_t klen = sizeof(k);
+	struct cb_node *node;
 
 	oidcpy(&k, oid);
 
@@ -58,7 +72,20 @@ bool oidtree_contains(struct oidtree *ot, const struct object_id *oid)
 	klen += BUILD_ASSERT_OR_ZERO(offsetof(struct object_id, hash) <
 				offsetof(struct object_id, algo));
 
-	return !!cb_lookup(&ot->tree, (const uint8_t *)&k, klen);
+	node = cb_lookup(&ot->tree, (const uint8_t *)&k, klen);
+	return node ? container_of(node, struct oidtree_node, base) : NULL;
+}
+
+bool oidtree_contains(struct oidtree *ot, const struct object_id *oid)
+{
+	struct oidtree_node *node = oidtree_lookup(ot, oid);
+	return node ? 1 : 0;
+}
+
+void *oidtree_get(struct oidtree *ot, const struct object_id *oid)
+{
+	struct oidtree_node *node = oidtree_lookup(ot, oid);
+	return node ? node->data : NULL;
 }
 
 struct oidtree_each_data {
@@ -82,7 +109,7 @@ static int iter(struct cb_node *n, void *cb_data)
 			return 0;
 	}
 
-	return data->cb(&node->key, data->cb_data);
+	return data->cb(&node->key, node->data, data->cb_data);
 }
 
 int oidtree_each(struct oidtree *ot, const struct object_id *prefix,
diff --git a/oidtree.h b/oidtree.h
index 2b7bad2e60..baa5a436ea 100644
--- a/oidtree.h
+++ b/oidtree.h
@@ -29,18 +29,26 @@ void oidtree_init(struct oidtree *ot);
  */
 void oidtree_clear(struct oidtree *ot);
 
-/* Insert the object ID into the tree. */
-void oidtree_insert(struct oidtree *ot, const struct object_id *oid);
+/*
+ * Insert the object ID into the tree and store the given pointer alongside
+ * with it. The data pointer of any preexisting entry will be overwritten.
+ */
+void oidtree_insert(struct oidtree *ot, const struct object_id *oid,
+		    void *data);
 
 /* Check whether the tree contains the given object ID. */
 bool oidtree_contains(struct oidtree *ot, const struct object_id *oid);
 
+/* Get the payload stored with the given object ID. */
+void *oidtree_get(struct oidtree *ot, const struct object_id *oid);
+
 /*
  * Callback function used for `oidtree_each()`. Returning a non-zero exit code
  * will cause iteration to stop. The exit code will be propagated to the caller
  * of `oidtree_each()`.
  */
 typedef int (*oidtree_each_cb)(const struct object_id *oid,
+			       void *node_data,
 			       void *cb_data);
 
 /*
diff --git a/t/unit-tests/u-oidtree.c b/t/unit-tests/u-oidtree.c
index d4d05c7dc3..f0d5ebb733 100644
--- a/t/unit-tests/u-oidtree.c
+++ b/t/unit-tests/u-oidtree.c
@@ -19,7 +19,7 @@ static int fill_tree_loc(struct oidtree *ot, const char *hexes[], size_t n)
 	for (size_t i = 0; i < n; i++) {
 		struct object_id oid;
 		cl_parse_any_oid(hexes[i], &oid);
-		oidtree_insert(ot, &oid);
+		oidtree_insert(ot, &oid, NULL);
 	}
 	return 0;
 }
@@ -38,9 +38,9 @@ struct expected_hex_iter {
 	const char *query;
 };
 
-static int check_each_cb(const struct object_id *oid, void *data)
+static int check_each_cb(const struct object_id *oid, void *node_data UNUSED, void *cb_data)
 {
-	struct expected_hex_iter *hex_iter = data;
+	struct expected_hex_iter *hex_iter = cb_data;
 	struct object_id expected;
 
 	cl_assert(hex_iter->i < hex_iter->expected_hexes.nr);
@@ -105,3 +105,23 @@ void test_oidtree__each(void)
 	check_each(&ot, "32100", "321", NULL);
 	check_each(&ot, "32", "320", "321", NULL);
 }
+
+void test_oidtree__insert_overwrites_data(void)
+{
+	struct object_id oid;
+	struct oidtree ot;
+	int a, b;
+
+	cl_parse_any_oid("1", &oid);
+
+	oidtree_init(&ot);
+
+	oidtree_insert(&ot, &oid, NULL);
+	cl_assert_equal_p(oidtree_get(&ot, &oid), NULL);
+	oidtree_insert(&ot, &oid, &a);
+	cl_assert_equal_p(oidtree_get(&ot, &oid), &a);
+	oidtree_insert(&ot, &oid, &b);
+	cl_assert_equal_p(oidtree_get(&ot, &oid), &b);
+
+	oidtree_clear(&ot);
+}