diff --git a/src/physics.F90 b/src/physics.F90
index 040da1cd00..4547b9c6c7 100644
--- a/src/physics.F90
+++ b/src/physics.F90
@@ -1023,7 +1023,7 @@ contains
     ! determine velocity vector of target nucleus
     v_target(1) = u*vt
     v_target(2) = v*vt
-    v_target(3) = W*vt
+    v_target(3) = w*vt
 
   end subroutine sample_target_velocity