diff --git a/src/engine/engine_derivative.c b/src/engine/engine_derivative.c
index d8b4c8bc..7bd35a95 100644
--- a/src/engine/engine_derivative.c
+++ b/src/engine/engine_derivative.c
@@ -1193,7 +1193,7 @@ void mjd_ellipsoidFluid(const mjModel* m, mjData* d, int bodyid) {
   for (int j=0; j < m->body_geomnum[bodyid]; j++) {
     const int geomid = m->body_geomadr[bodyid] + j;
 
-    mju_geomSemiAxes(m, geomid, semiaxes);
+    mju_geomSemiAxes(semiaxes, m->geom_size + 3*geomid, m->geom_type[geomid]);
 
     readFluidGeomInteraction(
       m->geom_fluid + mjNFLUID*geomid, &geom_interaction_coef,
diff --git a/src/engine/engine_passive.c b/src/engine/engine_passive.c
index 5b0d1b5b..5e222340 100644
--- a/src/engine/engine_passive.c
+++ b/src/engine/engine_passive.c
@@ -635,7 +635,7 @@ void mj_ellipsoidFluidModel(const mjModel* m, mjData* d, int bodyid) {
   for (int j=0; j < m->body_geomnum[bodyid]; j++) {
     const int geomid = m->body_geomadr[bodyid] + j;
 
-    mju_geomSemiAxes(m, geomid, semiaxes);
+    mju_geomSemiAxes(semiaxes, m->geom_size + 3*geomid, m->geom_type[geomid]);
 
     readFluidGeomInteraction(
       m->geom_fluid + mjNFLUID*geomid, &geom_interaction_coef,
diff --git a/src/engine/engine_util_misc.c b/src/engine/engine_util_misc.c
index 03435f48..1ca318fb 100644
--- a/src/engine/engine_util_misc.c
+++ b/src/engine/engine_util_misc.c
@@ -422,9 +422,8 @@ mjtNum mju_wrap(mjtNum wpnt[6], const mjtNum x0[3], const mjtNum x1[3],
 
 
 // all 3 semi-axes of a geom
-void mju_geomSemiAxes(const mjModel* m, int geom_id, mjtNum semiaxes[3]) {
-  mjtNum* size = m->geom_size + 3*geom_id;
-  switch ((mjtGeom) m->geom_type[geom_id]) {
+void mju_geomSemiAxes(mjtNum semiaxes[3], const mjtNum size[3], mjtGeom type) {
+  switch (type) {
   case mjGEOM_SPHERE:
     semiaxes[0] = size[0];
     semiaxes[1] = size[0];
diff --git a/src/engine/engine_util_misc.h b/src/engine/engine_util_misc.h
index f7f23782..9c6db647 100644
--- a/src/engine/engine_util_misc.h
+++ b/src/engine/engine_util_misc.h
@@ -51,7 +51,7 @@ MJAPI mjtNum mju_muscleDynamicsTimescale(mjtNum dctrl, mjtNum tau_act, mjtNum ta
 MJAPI mjtNum mju_muscleDynamics(mjtNum ctrl, mjtNum act, const mjtNum prm[3]);
 
 // all 3 semi-axes of a geom
-MJAPI void mju_geomSemiAxes(const mjModel* m, int geom_id, mjtNum semiaxes[3]);
+MJAPI void mju_geomSemiAxes(mjtNum semiaxes[3], const mjtNum size[3], mjtGeom type);
 
 // ----------------------------- Flex interpolation ------------------------------------------------