diff --git a/src/gravity/Default/gravity_iact.h b/src/gravity/Default/gravity_iact.h
index 8b706c7f63cff8ae588fdedad444441f98b0d58b..32d543a4214ad4af4a8128f12cf42ee5fc40abef 100644
--- a/src/gravity/Default/gravity_iact.h
+++ b/src/gravity/Default/gravity_iact.h
@@ -216,27 +216,21 @@ __attribute__((always_inline)) INLINE static void runner_iact_grav_pm_full(
 #if SELF_GRAVITY_MULTIPOLE_ORDER > 3
 
   /* 4th order contributions */
-  *f_x = m->M_004 * d.D_104 + m->M_013 * d.D_113 + m->M_022 * d.D_122
+  *f_x += m->M_004 * d.D_104 + m->M_013 * d.D_113 + m->M_022 * d.D_122
     + m->M_031 * d.D_131 + m->M_040 * d.D_140 + m->M_103 * d.D_203
     + m->M_112 * d.D_212 + m->M_121 * d.D_221 + m->M_130 * d.D_230
     + m->M_202 * d.D_302 + m->M_211 * d.D_311 + m->M_220 * d.D_320
     + m->M_301 * d.D_401 + m->M_310 * d.D_410 + m->M_400 * d.D_500;
-  *f_y = m->M_004 * d.D_014 + m->M_013 * d.D_023 + m->M_022 * d.D_032
+  *f_y += m->M_004 * d.D_014 + m->M_013 * d.D_023 + m->M_022 * d.D_032
     + m->M_031 * d.D_041 + m->M_040 * d.D_050 + m->M_103 * d.D_113
     + m->M_112 * d.D_122 + m->M_121 * d.D_131 + m->M_130 * d.D_140
     + m->M_202 * d.D_212 + m->M_211 * d.D_221 + m->M_220 * d.D_230
     + m->M_301 * d.D_311 + m->M_310 * d.D_320 + m->M_400 * d.D_410;
-  *f_z = m->M_004 * d.D_005 + m->M_013 * d.D_014 + m->M_022 * d.D_023
+  *f_z += m->M_004 * d.D_005 + m->M_013 * d.D_014 + m->M_022 * d.D_023
     + m->M_031 * d.D_032 + m->M_040 * d.D_041 + m->M_103 * d.D_104
     + m->M_112 * d.D_113 + m->M_121 * d.D_122 + m->M_130 * d.D_131
     + m->M_202 * d.D_203 + m->M_211 * d.D_212 + m->M_220 * d.D_221
     + m->M_301 * d.D_302 + m->M_310 * d.D_311 + m->M_400 * d.D_401;
-  *pot = m->M_004 * d.D_004 + m->M_013 * d.D_013 + m->M_022 * d.D_022
-    + m->M_031 * d.D_031 + m->M_040 * d.D_040 + m->M_103 * d.D_103
-    + m->M_112 * d.D_112 + m->M_121 * d.D_121 + m->M_130 * d.D_130
-    + m->M_202 * d.D_202 + m->M_211 * d.D_211 + m->M_220 * d.D_220
-    + m->M_301 * d.D_301 + m->M_310 * d.D_310 + m->M_400 * d.D_400;
-
 #endif
 
   /* Take care of the the sign convention */
@@ -343,27 +337,21 @@ __attribute__((always_inline)) INLINE static void runner_iact_grav_pm_truncated(
 #if SELF_GRAVITY_MULTIPOLE_ORDER > 3
 
   /* 4th order contributions */
-  *f_x = m->M_004 * d.D_104 + m->M_013 * d.D_113 + m->M_022 * d.D_122
+  *f_x += m->M_004 * d.D_104 + m->M_013 * d.D_113 + m->M_022 * d.D_122
     + m->M_031 * d.D_131 + m->M_040 * d.D_140 + m->M_103 * d.D_203
     + m->M_112 * d.D_212 + m->M_121 * d.D_221 + m->M_130 * d.D_230
     + m->M_202 * d.D_302 + m->M_211 * d.D_311 + m->M_220 * d.D_320
     + m->M_301 * d.D_401 + m->M_310 * d.D_410 + m->M_400 * d.D_500;
-  *f_y = m->M_004 * d.D_014 + m->M_013 * d.D_023 + m->M_022 * d.D_032
+  *f_y += m->M_004 * d.D_014 + m->M_013 * d.D_023 + m->M_022 * d.D_032
     + m->M_031 * d.D_041 + m->M_040 * d.D_050 + m->M_103 * d.D_113
     + m->M_112 * d.D_122 + m->M_121 * d.D_131 + m->M_130 * d.D_140
     + m->M_202 * d.D_212 + m->M_211 * d.D_221 + m->M_220 * d.D_230
     + m->M_301 * d.D_311 + m->M_310 * d.D_320 + m->M_400 * d.D_410;
-  *f_z = m->M_004 * d.D_005 + m->M_013 * d.D_014 + m->M_022 * d.D_023
+  *f_z += m->M_004 * d.D_005 + m->M_013 * d.D_014 + m->M_022 * d.D_023
     + m->M_031 * d.D_032 + m->M_040 * d.D_041 + m->M_103 * d.D_104
     + m->M_112 * d.D_113 + m->M_121 * d.D_122 + m->M_130 * d.D_131
     + m->M_202 * d.D_203 + m->M_211 * d.D_212 + m->M_220 * d.D_221
     + m->M_301 * d.D_302 + m->M_310 * d.D_311 + m->M_400 * d.D_401;
-  *pot = m->M_004 * d.D_004 + m->M_013 * d.D_013 + m->M_022 * d.D_022
-    + m->M_031 * d.D_031 + m->M_040 * d.D_040 + m->M_103 * d.D_103
-    + m->M_112 * d.D_112 + m->M_121 * d.D_121 + m->M_130 * d.D_130
-    + m->M_202 * d.D_202 + m->M_211 * d.D_211 + m->M_220 * d.D_220
-    + m->M_301 * d.D_301 + m->M_310 * d.D_310 + m->M_400 * d.D_400;
-
 #endif
   /* Take care of the the sign convention */
   *f_x *= -1.f;