diff --git a/src/space.c b/src/space.c
index ba70cb644387784451dfeeec1219fc14990820fd..159fa4a48f5b290d0161544e73c8d7d448c2cb89 100644
--- a/src/space.c
+++ b/src/space.c
@@ -480,6 +480,7 @@ void space_rebuild(struct space *s, double cell_max, int verbose) {
  * @brief Sort the particles and condensed particles according to the given
  *indices.
  *
+ * @param s The #space.
  * @param ind The indices with respect to which the parts are sorted.
  * @param N The number of parts
  * @param min Lowest index.