diff --git a/src/hydro/MAGMA/hydro_iact.h b/src/hydro/MAGMA/hydro_iact.h
index b7d979f7d2f90e2a0705daa9b341773c21c04e8e..d9da3766cc2fb993712f77c4d79458b7d6637ef0 100644
--- a/src/hydro/MAGMA/hydro_iact.h
+++ b/src/hydro/MAGMA/hydro_iact.h
@@ -327,7 +327,8 @@ __attribute__((always_inline)) INLINE static void runner_iact_nonsym_force(
           : 1.f;
 
   /* Van Leer limiter (eq. 21) */
-  const float fraction = 4.f * A_ij / ((1.f + A_ij) * (1.f + A_ij));
+  const float fraction =
+      (A_ij != -1.f) ? 4.f * A_ij / ((1.f + A_ij) * (1.f + A_ij)) : 1.f;
   const float Phi_ij = fmaxf(0.f, fminf(1.f, fraction)) * exp_term;
 
   /* Mid-point reconstruction, first order (eq. 17) */