diff --git a/src/backend/access/gin/ginvacuum.c b/src/backend/access/gin/ginvacuum.c
index 9dc8427a8e0..bfc07110067 100644
--- a/src/backend/access/gin/ginvacuum.c
+++ b/src/backend/access/gin/ginvacuum.c
@@ -153,6 +153,8 @@ ginDeletePage(GinVacuumState *gvs, BlockNumber deleteBlkno, BlockNumber leftBlkn
 	page = BufferGetPage(dBuffer);
 	rightlink = GinPageGetOpaque(page)->rightlink;
 
+	Assert(GinPageGetOpaque(BufferGetPage(lBuffer))->rightlink == deleteBlkno);
+
 	/*
 	 * Any insert which would have gone on the leaf block will now go to its
 	 * right sibling.
@@ -307,8 +309,21 @@ ginScanToDelete(GinVacuumState *gvs, BlockNumber blkno, bool isRoot,
 
 	if (isempty)
 	{
-		/* we never delete the left- or rightmost branch */
-		if (BufferIsValid(me->leftBuffer) && !GinPageRightMost(page))
+		/*
+		 * Proceed to the ginDeletePage() if target page is not the leftmost
+		 * or the rightmost page.
+		 *
+		 * leftBuffer is the target's left sibling according to the parent
+		 * level, which is not necessarily its left sibling in the sibling
+		 * link chain (the rightlinks stored on pages): the new right half of
+		 * an incompletely split page is in the sibling chain, but has no
+		 * downlink yet.  ginDeletePage isn't prepared to deal with that, so
+		 * we must refuse to delete when either the target or its left
+		 * sibling page is marked incompletely split.
+		 */
+		if (BufferIsValid(me->leftBuffer) && !GinPageRightMost(page) &&
+			!GinPageIsIncompleteSplit(page) &&
+			!GinPageIsIncompleteSplit(BufferGetPage(me->leftBuffer)))
 		{
 			Assert(!isRoot);
 			ginDeletePage(gvs, blkno, BufferGetBlockNumber(me->leftBuffer),