diff --git a/oidset.c b/oidset.c
index 5aac633c1f4..b36a2bae864 100644
--- a/oidset.c
+++ b/oidset.c
@@ -36,11 +36,6 @@ 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)
 {
 	oidset_parse_file_carefully(set, path, NULL, NULL);
diff --git a/oidset.h b/oidset.h
index 01f6560283c..ba4a5a2cd3a 100644
--- a/oidset.h
+++ b/oidset.h
@@ -57,7 +57,10 @@ 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);
+static inline int oidset_size(const struct oidset *set)
+{
+	return kh_size(&set->set);
+}
 
 /**
  * Remove all entries from the oidset, freeing any resources associated with