diff --git a/source/Simulator/DelayedFluidSimulator.cpp b/source/Simulator/DelayedFluidSimulator.cpp
index b69718977..6cc982e3d 100644
--- a/source/Simulator/DelayedFluidSimulator.cpp
+++ b/source/Simulator/DelayedFluidSimulator.cpp
@@ -86,7 +86,7 @@ void cDelayedFluidSimulator::AddBlock(int a_BlockX, int a_BlockY, int a_BlockZ,
 		return;
 	}
 	
-	if (a_Chunk == NULL)
+	if ((a_Chunk == NULL) || !a_Chunk->IsValid())
 	{
 		return;
 	}
diff --git a/source/Simulator/FireSimulator.cpp b/source/Simulator/FireSimulator.cpp
index 0e6c1fac1..587f45306 100644
--- a/source/Simulator/FireSimulator.cpp
+++ b/source/Simulator/FireSimulator.cpp
@@ -187,7 +187,7 @@ bool cFireSimulator::IsForever(BLOCKTYPE a_BlockType)
 
 void cFireSimulator::AddBlock(int a_BlockX, int a_BlockY, int a_BlockZ, cChunk * a_Chunk)
 {
-	if (a_Chunk == NULL)
+	if ((a_Chunk == NULL) || !a_Chunk->IsValid())
 	{
 		return;
 	}
diff --git a/source/Simulator/SandSimulator.cpp b/source/Simulator/SandSimulator.cpp
index ed1a2bf52..e6026be83 100644
--- a/source/Simulator/SandSimulator.cpp
+++ b/source/Simulator/SandSimulator.cpp
@@ -93,7 +93,7 @@ bool cSandSimulator::IsAllowedBlock(BLOCKTYPE a_BlockType)
 
 void cSandSimulator::AddBlock(int a_BlockX, int a_BlockY, int a_BlockZ, cChunk * a_Chunk)
 {
-	if (a_Chunk == NULL)
+	if ((a_Chunk == NULL) || !a_Chunk->IsValid())
 	{
 		return;
 	}