diff --git a/src/p_mobj.c b/src/p_mobj.c
index 635d4f42b..f8f4ee2a6 100644
--- a/src/p_mobj.c
+++ b/src/p_mobj.c
@@ -13277,6 +13277,23 @@ static boolean P_SetupSpawnedMapThing(mapthing_t *mthing, mobj_t *mobj, boolean
 	return true;
 }
 
+// Pre-UDMF backwards compatibility stuff. Remove for 2.3
+static void P_SetAmbush(mapthing_t *mthing, mobj_t *mobj)
+{
+	if (mobj->type == MT_NIGHTSBUMPER
+		|| mobj->type == MT_AXIS
+		|| mobj->type == MT_AXISTRANSFER
+		|| mobj->type == MT_AXISTRANSFERLINE
+		|| mobj->type == MT_NIGHTSBUMPER
+		|| mobj->type == MT_STARPOST)
+		return;
+
+	if ((mthing->options & MTF_OBJECTSPECIAL) && (mobj->flags & MF_PUSHABLE))
+		return;
+
+	mobj->flags2 |= MF2_AMBUSH;
+}
+
 static mobj_t *P_SpawnMobjFromMapThing(mapthing_t *mthing, fixed_t x, fixed_t y, fixed_t z, mobjtype_t i)
 {
 	mobj_t *mobj = NULL;
@@ -13299,6 +13316,9 @@ static mobj_t *P_SpawnMobjFromMapThing(mapthing_t *mthing, fixed_t x, fixed_t y,
 
 	mthing->mobj = mobj;
 
+	if (!udmf && (mthing->options & MTF_AMBUSH))
+		P_SetAmbush(mthing, mobj);
+
 	// Generic reverse gravity for individual objects flag.
 	if (mthing->options & MTF_OBJECTFLIP)
 	{