diff --git a/src/gswe-moment.c b/src/gswe-moment.c
index b54bb2d..0a81ad3 100644
--- a/src/gswe-moment.c
+++ b/src/gswe-moment.c
@@ -779,7 +779,7 @@ gswe_moment_get_house(GsweMoment *moment, gdouble position, GError **err)
  *
  * Returns: (transfer none): @planet's data
  */
-GswePlanetData *
+const GswePlanetData *
 gswe_moment_get_planet(GsweMoment *moment, GswePlanet planet, GError **err)
 {
     GswePlanetData *planet_data = (GswePlanetData *)(g_list_find_custom(moment->priv->planet_list, &planet, find_by_planet_id)->data);
@@ -877,7 +877,7 @@ gswe_moment_get_quality_points(GsweMoment *moment, GsweQuality quality)
  *
  * Returns: (transfer none): a #GsweMoonPhaseData representing the phase of the Moon
  */
-GsweMoonPhaseData *
+const GsweMoonPhaseData *
 gswe_moment_get_moon_phase(GsweMoment *moment, GError **err)
 {
     gdouble difference,
diff --git a/src/gswe-moment.h b/src/gswe-moment.h
index d953f06..8cfa624 100644
--- a/src/gswe-moment.h
+++ b/src/gswe-moment.h
@@ -137,10 +137,10 @@ gboolean gswe_moment_has_planet(GsweMoment *moment, GswePlanet planet);
 void gswe_moment_add_planet(GsweMoment *moment, GswePlanet planet);
 void gswe_moment_add_all_planets(GsweMoment *moment);
 GList *gswe_moment_get_planets(GsweMoment *moment);
-GswePlanetData *gswe_moment_get_planet(GsweMoment *moment, GswePlanet planet, GError **err);
+const GswePlanetData *gswe_moment_get_planet(GsweMoment *moment, GswePlanet planet, GError **err);
 guint gswe_moment_get_element_points(GsweMoment *moment, GsweElement element);
 guint gswe_moment_get_quality_points(GsweMoment *moment, GsweQuality quality);
-GsweMoonPhaseData *gswe_moment_get_moon_phase(GsweMoment *moment, GError **err);
+const GsweMoonPhaseData *gswe_moment_get_moon_phase(GsweMoment *moment, GError **err);
 GList *gswe_moment_get_all_aspects(GsweMoment *moment);
 GList *gswe_moment_get_planet_aspects(GsweMoment *moment, GswePlanet planet, GError **err);
 GList *gswe_moment_get_all_antiscia(GsweMoment *moment);