diff --git a/source/Blocks/BlockDirt.h b/source/Blocks/BlockDirt.h
index 73bc28dc5..6cec5d99e 100644
--- a/source/Blocks/BlockDirt.h
+++ b/source/Blocks/BlockDirt.h
@@ -34,11 +34,14 @@ public:
 		}
 		
 		// Grass becomes dirt if there is something on top of it:
-		BLOCKTYPE Above = a_World->GetBlock(a_BlockX, a_BlockY + 1, a_BlockZ);
-		if (!g_BlockTransparent[Above] && !g_BlockOneHitDig[Above])
+		if (a_BlockY < cChunkDef::Height - 1)
 		{
-			a_World->FastSetBlock(a_BlockX, a_BlockY, a_BlockZ, E_BLOCK_DIRT, 0);
-			return;
+			BLOCKTYPE Above = a_World->GetBlock(a_BlockX, a_BlockY + 1, a_BlockZ);
+			if (!g_BlockTransparent[Above] && !g_BlockOneHitDig[Above])
+			{
+				a_World->FastSetBlock(a_BlockX, a_BlockY, a_BlockZ, E_BLOCK_DIRT, 0);
+				return;
+			}
 		}
 		
 		// Grass spreads to adjacent blocks:
@@ -51,6 +54,11 @@ public:
 	
 			BLOCKTYPE  DestBlock;
 			NIBBLETYPE DestMeta;
+			if ((a_BlockY + OfsY < 0) || (a_BlockY + OfsY >= cChunkDef::Height - 1))
+			{
+				// Y Coord out of range
+				continue;
+			}
 			bool IsValid = a_World->GetBlockTypeMeta(a_BlockX + OfsX, a_BlockY + OfsY, a_BlockZ + OfsZ, DestBlock, DestMeta);
 			if (!IsValid || (DestBlock != E_BLOCK_DIRT))
 			{
diff --git a/source/LightingThread.cpp b/source/LightingThread.cpp
index 258fd7dd4..d7e60e458 100644
--- a/source/LightingThread.cpp
+++ b/source/LightingThread.cpp
@@ -407,9 +407,12 @@ void cLightingThread::PrepareSkyLight(void)
 			}
 			
 			// Add Current as a seed:
-			int CurrentIdx = idx + Current * BlocksPerYLayer;
-			m_IsSeed1[CurrentIdx] = true;
-			m_SeedIdx1[m_NumSeeds++] = CurrentIdx;
+			if (Current < cChunkDef::Height)
+			{
+				int CurrentIdx = idx + Current * BlocksPerYLayer;
+				m_IsSeed1[CurrentIdx] = true;
+				m_SeedIdx1[m_NumSeeds++] = CurrentIdx;
+			}
 			
 			// Add seed from Current up to the highest neighbor:
 			for (int y = Current + 1, Index = idx + y * BlocksPerYLayer; y < MaxNeighbor; y++, Index += BlocksPerYLayer)