diff --git a/oidset.c b/oidset.c
index f63ce818f6..15d4e18c37 100644
--- a/oidset.c
+++ b/oidset.c
@@ -36,6 +36,11 @@ void oidset_clear(struct oidset *set)
 	oidset_init(set, 0);
 }
 
+int oidset_size(struct oidset *set)
+{
+	return kh_size(&set->set);
+}
+
 void oidset_parse_file(struct oidset *set, const char *path)
 {
 	FILE *fp;
diff --git a/oidset.h b/oidset.h
index 5346563b0b..80c3a347f9 100644
--- a/oidset.h
+++ b/oidset.h
@@ -55,6 +55,11 @@ int oidset_insert(struct oidset *set, const struct object_id *oid);
  */
 int oidset_remove(struct oidset *set, const struct object_id *oid);
 
+/**
+ * Returns the number of oids in the set.
+ */
+int oidset_size(struct oidset *set);
+
 /**
  * Remove all entries from the oidset, freeing any resources associated with
  * it.