diff --git a/src/gamedata/r_defs.h b/src/gamedata/r_defs.h
index e940d80abd..bf0f6be4b9 100644
--- a/src/gamedata/r_defs.h
+++ b/src/gamedata/r_defs.h
@@ -40,7 +40,6 @@
 #include "r_sky.h"
 #include "p_terrain.h"
 #include "p_effect.h"
-#include "vm.h"
 
 #include "hwrenderer/data/buffers.h"
 
@@ -1032,13 +1031,11 @@ public:
 
 	void SetPlaneReflectivity(int pos, double val)
 	{
-		if (pos < 0 || pos > 1) ThrowAbortException(X_ARRAY_OUT_OF_BOUNDS, "pos must be either 0 or 1");
 		reflect[pos] = val;
 	}
 
 	double GetPlaneReflectivity(int pos)
 	{
-		if (pos < 0 || pos > 1) ThrowAbortException(X_ARRAY_OUT_OF_BOUNDS, "pos must be either 0 or 1");
 		return reflect[pos];
 	}
 
diff --git a/src/scripting/vmthunks.cpp b/src/scripting/vmthunks.cpp
index b8241fc112..0c738a424a 100644
--- a/src/scripting/vmthunks.cpp
+++ b/src/scripting/vmthunks.cpp
@@ -871,6 +871,7 @@ DEFINE_ACTION_FUNCTION_NATIVE(_Sector, SetXOffset, SetXOffset)
 
  static void SetPlaneReflectivity(sector_t* self, int pos, double val)
  {
+	 if (pos < 0 || pos > 1) ThrowAbortException(X_ARRAY_OUT_OF_BOUNDS, "pos must be either 0 or 1");
 	 self->SetPlaneReflectivity(pos, val);
  }
 
@@ -885,6 +886,7 @@ DEFINE_ACTION_FUNCTION_NATIVE(_Sector, SetXOffset, SetXOffset)
 
  static double GetPlaneReflectivity(sector_t* self, int pos)
  {
+	 if (pos < 0 || pos > 1) ThrowAbortException(X_ARRAY_OUT_OF_BOUNDS, "pos must be either 0 or 1");
 	 return self->GetPlaneReflectivity(pos);
  }