diff --git a/src/hydro/Default/hydro.h b/src/hydro/Default/hydro.h
index b4ed2daf385691958d5849b0ac2d651ac6f98d34..9c88f357dc831d618ae52a095d15daff8ca3d92e 100644
--- a/src/hydro/Default/hydro.h
+++ b/src/hydro/Default/hydro.h
@@ -27,7 +27,7 @@
  *
  */
 __attribute__((always_inline)) INLINE static float hydro_compute_timestep(
-    struct part* p, struct xpart* xp,
+    const struct part* p, const struct xpart* xp,
     const struct hydro_props* hydro_properties) {
 
   const float CFL_condition = hydro_properties->CFL_condition;
diff --git a/src/hydro/Minimal/hydro.h b/src/hydro/Minimal/hydro.h
index 01957065cf5b1d89bb839449ac60b9ec965c2c47..9c7629fec1265f9ba0becd3023df339aa706ad0b 100644
--- a/src/hydro/Minimal/hydro.h
+++ b/src/hydro/Minimal/hydro.h
@@ -31,7 +31,7 @@
  *
  */
 __attribute__((always_inline)) INLINE static float hydro_compute_timestep(
-    struct part* p, struct xpart* xp,
+    const struct part* p, const struct xpart* xp,
     const struct hydro_props* hydro_properties) {
 
   const float CFL_condition = hydro_properties->CFL_condition;