diff --git a/src/p_map.c b/src/p_map.c
index 1116ae06a..ab6e62edd 100644
--- a/src/p_map.c
+++ b/src/p_map.c
@@ -4385,15 +4385,15 @@ static boolean P_CheckSectorPolyObjects(sector_t *sector, boolean realcrush, boo
 			{
 				mobj_t *mo;
 				blocknode_t *block;
+				blocknode_t *next = NULL;
 
 				if (x < 0 || y < 0 || x >= bmapwidth || y >= bmapheight)
 					continue;
 
-				block = blocklinks[y * bmapwidth + x];
-
-				for (; block; block = block->mnext)
+				for (block = blocklinks[y * bmapwidth + x]; block != NULL; block = next)
 				{
 					mo = block->mobj;
+					next = block->mnext;
 
 					// Monster Iestyn: do we need to check if a mobj has already been checked? ...probably not I suspect
 					if (!P_MobjInsidePolyobj(po, mo))
diff --git a/src/p_maputl.c b/src/p_maputl.c
index 6842677b3..5398fd7a4 100644
--- a/src/p_maputl.c
+++ b/src/p_maputl.c
@@ -1058,9 +1058,9 @@ boolean P_BlockThingsIterator(INT32 x, INT32 y, boolean (*func)(mobj_t *))
 		return true;
 
 	// Check interaction with the objects in the blockmap.
-	for (block = blocklinks[y*bmapwidth + x]; block; block = next)
+	for (block = blocklinks[y*bmapwidth + x]; block != NULL; block = next)
 	{
-		next = block->mnext; // We want to note our reference to mnext here in case the object gets removed!
+		next = block->mnext; // We want to note our reference to mnext here!
 
 		if (!func(block->mobj))
 			return false;
diff --git a/src/p_polyobj.c b/src/p_polyobj.c
index 168fca61f..1d651dcd2 100644
--- a/src/p_polyobj.c
+++ b/src/p_polyobj.c
@@ -878,15 +878,15 @@ static void Polyobj_carryThings(polyobj_t *po, fixed_t dx, fixed_t dy)
 		{
 			mobj_t *mo;
 			blocknode_t *block;
+			blocknode_t *next = NULL;
 
 			if (x < 0 || y < 0 || x >= bmapwidth || y >= bmapheight)
 				continue;
 
-			block = blocklinks[y * bmapwidth + x];
-
-			for (; block; block = block->mnext)
+			for (block = blocklinks[y * bmapwidth + x]; block != NULL; block = next)
 			{
 				mo = block->mobj;
+				next = block->mnext;
 
 				if (mo->lastlook == pomovecount)
 					continue;
@@ -942,9 +942,11 @@ static INT32 Polyobj_clipThings(polyobj_t *po, line_t *line)
 			{
 				mobj_t *mo = NULL;
 				blocknode_t *block = blocklinks[y * bmapwidth + x];
+				blocknode_t *next = NULL;
 
-				for (; block; block = block->mnext)
+				for (; block != NULL; block = next)
 				{
+					next = block->mnext;
 					mo = block->mobj;
 
 					// Don't scroll objects that aren't affected by gravity
@@ -1115,15 +1117,15 @@ static void Polyobj_rotateThings(polyobj_t *po, vector2_t origin, angle_t delta,
 		{
 			mobj_t *mo;
 			blocknode_t *block;
+			blocknode_t *next = NULL;
 
 			if (x < 0 || y < 0 || x >= bmapwidth || y >= bmapheight)
 				continue;
 
-			block = blocklinks[y * bmapwidth + x];
-
-			for (; block; block = block->mnext)
+			for (block = blocklinks[y * bmapwidth + x]; block != NULL; block = next)
 			{
 				mo = block->mobj;
+				next = block->mnext;
 
 				if (mo->lastlook == pomovecount)
 					continue;