diff --git a/docs/rh-log.txt b/docs/rh-log.txt
index 492590474..74c60b1f4 100644
--- a/docs/rh-log.txt
+++ b/docs/rh-log.txt
@@ -1,4 +1,9 @@
-April 7, 2009  (Changes by Graf Zahl)
+April 8, 2009
+- Performance optimization for FBlockThingsIterator::Next(): Actors that
+  exist in only one block don't need to be added to the CheckArray or
+  scanned for in it.
+
+April 7, 2009  (Changes by Graf Zahl)
 - added some default definitions for constants that may miss in some headers.
 - replaced __va_copy with va_copy per Chris's suggestion.
 - replaced #include <malloc.h> with #include <stdlib.h> where possible.
diff --git a/src/p_maputl.cpp b/src/p_maputl.cpp
index 194d8950f..775a408b0 100644
--- a/src/p_maputl.cpp
+++ b/src/p_maputl.cpp
@@ -830,15 +830,20 @@ void FBlockThingsIterator::StartBlock(int x, int y)
 
 AActor *FBlockThingsIterator::Next()
 {
-	while (true)
+	for (;;)
 	{
 		while (block != NULL)
 		{
 			AActor *me = block->Me;
+			FBlockNode *mynode = block;
 			int i;
 
 			block = block->NextActor;
 			// Don't recheck things that were already checked
+			if (mynode->NextBlock == NULL && mynode->PrevBlock == &me->BlockNode)
+			{ // This actor doesn't span blocks, so we know it can only ever be checked once.
+				return me;
+			}
 			for (i = (int)CheckArray.Size() - 1; i >= checkindex; --i)
 			{
 				if (CheckArray[i] == me)