*** a/src/backend/utils/adt/rangetypes_spgist.c
--- b/src/backend/utils/adt/rangetypes_spgist.c
***************
*** 104,109 **** getQuadrant(TypeCacheEntry *typcache, RangeType *centroid, RangeType *tst)
--- 104,112 ----
  
  	range_deserialize(typcache, centroid, &centroidLower, &centroidUpper,
  					  &centroidEmpty);
+ 
+ 	Assert(!centroidEmpty);
+ 
  	range_deserialize(typcache, tst, &lower, &upper, &empty);
  
  	if (empty)
***************
*** 138,143 **** spg_range_quad_choose(PG_FUNCTION_ARGS)
--- 141,158 ----
  	int16		quadrant;
  	TypeCacheEntry *typcache;
  
+ 	/* if there is no prefix, they must be all the same */
+ 	Assert(in->hasPrefix || in->allTheSame);
+ 	/*
+ 	 * If there are two nodes, it must either be the root or at level 1, and
+ 	 * there must be no prefix.
+ 	 */
+ 	Assert(in->nNodes != 2 ||
+ 		   (!in->hasPrefix && (in->level == 0 || in->level == 1)));
+ 	/* if there are 4 or 5 nodes, there must be a prefix */
+ 	Assert(in->nNodes != 4 || in->hasPrefix);
+ 	Assert(in->nNodes != 5 || (in->hasPrefix && in->level == 0));
+ 
  	if (in->allTheSame)
  	{
  		out->resultType = spgMatchNode;
***************
*** 156,161 **** spg_range_quad_choose(PG_FUNCTION_ARGS)
--- 171,178 ----
  	 */
  	if (!in->hasPrefix)
  	{
+ 		Assert(false);
+ 
  		out->resultType = spgMatchNode;
  		if (RangeIsEmpty(inRange))
  			out->result.matchNode.nodeN = 0;
***************
*** 232,237 **** spg_range_quad_picksplit(PG_FUNCTION_ARGS)
--- 249,261 ----
  	nonEmptyCount = j;
  
  	/*
+ 	 * Only the root mixes empty and non-empty tuples.
+ 	 */
+ 	Assert(nonEmptyCount == 0 ||
+ 		   nonEmptyCount == in->nTuples ||
+ 		   in->level == 0);
+ 
+ 	/*
  	 * All the ranges are empty. The best we can do is to construct an inner
  	 * node with no centroid, and put all ranges into node 0. If non-empty
  	 * ranges are added later, they will be routed to node 1.
***************
*** 315,320 **** spg_range_quad_inner_consistent(PG_FUNCTION_ARGS)
--- 339,356 ----
  	 */
  	bool		needPrevious = false;
  
+ 	/* if there is no prefix, they must be all the same */
+ 	Assert(in->hasPrefix || in->allTheSame);
+ 	/*
+ 	 * If there are two nodes, it must either be the root or at level 1, and
+ 	 * there must be no prefix.
+ 	 */
+ 	Assert(in->nNodes != 2 ||
+ 		   (!in->hasPrefix && (in->level == 0 || in->level == 1)));
+ 	/* if there are 4 or 5 nodes, there must be a prefix */
+ 	Assert(in->nNodes != 4 || in->hasPrefix);
+ 	Assert(in->nNodes != 5 || (in->hasPrefix && in->level == 0));
+ 
  	if (in->allTheSame)
  	{
  		/* Report that all nodes should be visited */
***************
*** 327,332 **** spg_range_quad_inner_consistent(PG_FUNCTION_ARGS)
--- 363,370 ----
  
  	if (!in->hasPrefix)
  	{
+ 		Assert(false);
+ 
  		/*
  		 * No centroid on this inner node. Such a node has two child nodes,
  		 * the first for empty ranges, and the second for non-empty ones.