diff --git a/odb/source-inmemory.c b/odb/source-inmemory.c
index d1674836cc..a8eba373ee 100644
--- a/odb/source-inmemory.c
+++ b/odb/source-inmemory.c
@@ -165,6 +165,44 @@ static int odb_source_inmemory_for_each_object(struct odb_source *source,
 			    odb_source_inmemory_for_each_object_cb, &payload);
 }
 
+struct find_abbrev_len_data {
+	const struct object_id *oid;
+	unsigned len;
+};
+
+static int find_abbrev_len_cb(const struct object_id *oid,
+			      struct object_info *oi UNUSED,
+			      void *cb_data)
+{
+	struct find_abbrev_len_data *data = cb_data;
+	unsigned len = oid_common_prefix_hexlen(oid, data->oid);
+	if (len != hash_algos[oid->algo].hexsz && len >= data->len)
+		data->len = len + 1;
+	return 0;
+}
+
+static int odb_source_inmemory_find_abbrev_len(struct odb_source *source,
+					       const struct object_id *oid,
+					       unsigned min_len,
+					       unsigned *out)
+{
+	struct odb_for_each_object_options opts = {
+		.prefix = oid,
+		.prefix_hex_len = min_len,
+	};
+	struct find_abbrev_len_data data = {
+		.oid = oid,
+		.len = min_len,
+	};
+	int ret;
+
+	ret = odb_source_inmemory_for_each_object(source, NULL, find_abbrev_len_cb,
+						  &data, &opts);
+	*out = data.len;
+
+	return ret;
+}
+
 static int odb_source_inmemory_write_object(struct odb_source *source,
 					    const void *buf, unsigned long len,
 					    enum object_type type,
@@ -271,6 +309,7 @@ struct odb_source_inmemory *odb_source_inmemory_new(struct object_database *odb)
 	source->base.read_object_info = odb_source_inmemory_read_object_info;
 	source->base.read_object_stream = odb_source_inmemory_read_object_stream;
 	source->base.for_each_object = odb_source_inmemory_for_each_object;
+	source->base.find_abbrev_len = odb_source_inmemory_find_abbrev_len;
 	source->base.write_object = odb_source_inmemory_write_object;
 	source->base.write_object_stream = odb_source_inmemory_write_object_stream;