diff --git a/src/p_local.h b/src/p_local.h
index 5b3d7f7b2..7ced38f2f 100644
--- a/src/p_local.h
+++ b/src/p_local.h
@@ -46,9 +46,7 @@
 #define BMBOUNDFIX(xl, xh, yl, yh) {if (xl > xh) xl = 0; if (yl > yh) yl = 0;}
 
 // MAXRADIUS is for precalculated sector block boxes
-// the spider demon is larger,
-// but we do not have any moving sectors nearby
-#define MAXRADIUS (32*FRACUNIT)
+#define MAXRADIUS (MAPBLOCKSIZE >> 1)
 
 // max Z move up or down without jumping
 // above this, a height difference is considered as a 'dropoff'
diff --git a/src/p_mobj.c b/src/p_mobj.c
index 6ffc84c66..6ab24c5d2 100644
--- a/src/p_mobj.c
+++ b/src/p_mobj.c
@@ -12406,7 +12406,7 @@ static boolean P_SetupSpawnedMapThing(mapthing_t *mthing, mobj_t *mobj, boolean
 		// Ambush = double size (grounded) / half size (aerial)
 		if (!(mthing->options & MTF_AMBUSH) == !P_IsObjectOnGround(mobj))
 		{
-			mobj->extravalue1 = min(mobj->extravalue1 << 1, FixedDiv(64*FRACUNIT, mobj->info->radius)); // don't make them larger than the blockmap can handle
+			mobj->extravalue1 = min(mobj->extravalue1 << 1, FixedDiv(MAPBLOCKSIZE, mobj->info->radius)); // don't make them larger than the blockmap can handle
 			mobj->scalespeed <<= 1;
 		}
 		break;