diff --git a/src/mcx_core.cu b/src/mcx_core.cu
index cf28eeee..3f4a023b 100644
--- a/src/mcx_core.cu
+++ b/src/mcx_core.cu
@@ -935,6 +935,11 @@ __device__ inline void rotatevector2d(MCXdir* v, float stheta, float ctheta) {
                             v->nscat
                         );
 
+    float tmp0 = rsqrtf(v->x * v->x + v->y * v->y + v->z * v->z);
+    v->x *= tmp0;
+    v->y *= tmp0;
+    v->z *= tmp0;
+
     GPUDEBUG(("new dir: %10.5e %10.5e %10.5e\n", v->x, v->y, v->z));
 }
 
@@ -964,6 +969,11 @@ __device__ inline void rotatevector(MCXdir* v, float stheta, float ctheta, float
         *((float4*)v) = float4(stheta * cphi, stheta * sphi, (v->z > 0.f) ? ctheta : -ctheta, v->nscat);
     }
 
+    float tmp0 = rsqrtf(v->x * v->x + v->y * v->y + v->z * v->z);
+    v->x *= tmp0;
+    v->y *= tmp0;
+    v->z *= tmp0;
+
     GPUDEBUG(("new dir: %10.5e %10.5e %10.5e\n", v->x, v->y, v->z));
 }