diff --git a/src/backend/access/gist/gistproc.c b/src/backend/access/gist/gistproc.c
index d474612b77..19a7d5ef2b 100644
--- a/src/backend/access/gist/gistproc.c
+++ b/src/backend/access/gist/gistproc.c
@@ -1237,11 +1237,15 @@ computeDistance(bool isLeaf, BOX *box, Point *point)
 	else if (point->x <= box->high.x && point->x >= box->low.x)
 	{
 		/* point is over or below box */
-		Assert(box->low.y <= box->high.y);
+		Assert(box->low.y <= box->high.y
+			   || isnan(box->low.y) || isnan(box->high.y));
+
 		if (point->y > box->high.y)
 			result = float8_mi(point->y, box->high.y);
 		else if (point->y < box->low.y)
 			result = float8_mi(box->low.y, point->y);
+		else if (isnan(point->y) || isnan(box->high.y) || isnan(box->low.y))
+			result = get_float8_nan();
 		else
 			elog(ERROR, "inconsistent point values");
 	}