diff --git a/source/simulation2/helpers/Grid.h b/source/simulation2/helpers/Grid.h
index ba5bf77ec1..6ac0a73045 100644
--- a/source/simulation2/helpers/Grid.h
+++ b/source/simulation2/helpers/Grid.h
@@ -88,9 +88,8 @@ public:
 #if GRID_BOUNDS_DEBUG
 		ENSURE(g.m_W == m_W && g.m_H == m_H);
 #endif
-		for (int j=0; j < m_H; ++j)
-			for (int i=0; i < m_W; ++i)
-				m_Data[j*m_W + i] += g.m_Data[j*m_W + i];
+		for (int i=0; i < m_H*m_W; ++i)
+			m_Data[i] += g.m_Data[i];
 	}
 
 	void set(int i, int j, const T& value)