diff --git a/doc/src/sgml/indexam.sgml b/doc/src/sgml/indexam.sgml
index 80f55da87b364a9511ca2b8c71ceccc37991322c..a6e4466e8a15ba916a42b18b7eaee9c726f5f2b8 100644
--- a/doc/src/sgml/indexam.sgml
+++ b/doc/src/sgml/indexam.sgml
@@ -396,7 +396,8 @@ amgettuple (IndexScanDesc scan,
    row), then on success it must also check
    <literal>scan-&gt;xs_want_itup</>, and if that is true it must return
    the original indexed data for the index entry, in the form of an
-   <structname>IndexTuple</> pointer stored at <literal>scan-&gt;xs_itup</>.
+   <structname>IndexTuple</> pointer stored at <literal>scan-&gt;xs_itup</>,
+   with tuple descriptor <literal>scan-&gt;xs_itupdesc</>.
    (Management of the data referenced by the pointer is the access method's
    responsibility.  The data must remain good at least until the next
    <function>amgettuple</>, <function>amrescan</>, or <function>amendscan</>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 236e48912bbaad5d88434b4a5d3d57ea09321cef..1732ef7bfe5544a3c6bf5269445fcce8c7aa9168 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -112,6 +112,7 @@ RelationGetIndexScan(Relation indexRelation, int nkeys, int norderbys)
 	scan->opaque = NULL;
 
 	scan->xs_itup = NULL;
+	scan->xs_itupdesc = NULL;
 
 	ItemPointerSetInvalid(&scan->xs_ctup.t_self);
 	scan->xs_ctup.t_data = NULL;
diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c
index 60b7f599a74272df11f45a9f6f75ad119cce159d..f3a1d256a059dbee332ad363b8ccbe651cfacb31 100644
--- a/src/backend/access/nbtree/nbtree.c
+++ b/src/backend/access/nbtree/nbtree.c
@@ -433,12 +433,15 @@ btbeginscan(PG_FUNCTION_ARGS)
 
 	/*
 	 * We don't know yet whether the scan will be index-only, so we do not
-	 * allocate the tuple workspace arrays until btrescan.
+	 * allocate the tuple workspace arrays until btrescan.  However, we set up
+	 * scan->xs_itupdesc whether we'll need it or not, since that's so cheap.
 	 */
 	so->currTuples = so->markTuples = NULL;
 	so->currPos.nextTupleOffset = 0;
 	so->markPos.nextTupleOffset = 0;
 
+	scan->xs_itupdesc = RelationGetDescr(rel);
+
 	scan->opaque = so;
 
 	PG_RETURN_POINTER(scan);
diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index e3742cf71d05c88e8e7a557144261eacc5837654..a07686d4638c810aef871c99468009673f910665 100644
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -36,7 +36,7 @@
 
 static TupleTableSlot *IndexOnlyNext(IndexOnlyScanState *node);
 static void StoreIndexTuple(TupleTableSlot *slot, IndexTuple itup,
-							Relation indexRel);
+				TupleDesc itupdesc);
 
 
 /* ----------------------------------------------------------------
@@ -114,7 +114,7 @@ IndexOnlyNext(IndexOnlyScanState *node)
 		/*
 		 * Fill the scan tuple slot with data from the index.
 		 */
-		StoreIndexTuple(slot, scandesc->xs_itup, scandesc->indexRelation);
+		StoreIndexTuple(slot, scandesc->xs_itup, scandesc->xs_itupdesc);
 
 		/*
 		 * If the index was lossy, we have to recheck the index quals.
@@ -151,25 +151,25 @@ IndexOnlyNext(IndexOnlyScanState *node)
  * right now we don't need it elsewhere.
  */
 static void
-StoreIndexTuple(TupleTableSlot *slot, IndexTuple itup, Relation indexRel)
+StoreIndexTuple(TupleTableSlot *slot, IndexTuple itup, TupleDesc itupdesc)
 {
-	TupleDesc	indexDesc = RelationGetDescr(indexRel);
-	int			nindexatts = indexDesc->natts;
+	int			nindexatts = itupdesc->natts;
 	Datum	   *values = slot->tts_values;
 	bool	   *isnull = slot->tts_isnull;
 	int			i;
 
 	/*
-	 * Note: we must use the index relation's tupdesc in index_getattr, not
+	 * Note: we must use the tupdesc supplied by the AM in index_getattr, not
 	 * the slot's tupdesc, in case the latter has different datatypes (this
 	 * happens for btree name_ops in particular).  They'd better have the same
-	 * number of columns though.
+	 * number of columns though, as well as being datatype-compatible which
+	 * is something we can't so easily check.
 	 */
 	Assert(slot->tts_tupleDescriptor->natts == nindexatts);
 
 	ExecClearTuple(slot);
 	for (i = 0; i < nindexatts; i++)
-		values[i] = index_getattr(itup, i + 1, indexDesc, &isnull[i]);
+		values[i] = index_getattr(itup, i + 1, itupdesc, &isnull[i]);
 	ExecStoreVirtualTuple(slot);
 }
 
diff --git a/src/include/access/relscan.h b/src/include/access/relscan.h
index d48bbf865ea1a180d225d3059667224b894e0065..b2dea15a63810bc010ab9dd0aefbd06d8fd94863 100644
--- a/src/include/access/relscan.h
+++ b/src/include/access/relscan.h
@@ -17,6 +17,7 @@
 #include "access/genam.h"
 #include "access/heapam.h"
 #include "access/itup.h"
+#include "access/tupdesc.h"
 
 
 typedef struct HeapScanDescData
@@ -80,6 +81,7 @@ typedef struct IndexScanDescData
 
 	/* in an index-only scan, this is valid after a successful amgettuple */
 	IndexTuple	xs_itup;		/* index tuple returned by AM */
+	TupleDesc	xs_itupdesc;	/* rowtype descriptor of xs_itup */
 
 	/* xs_ctup/xs_cbuf/xs_recheck are valid after a successful index_getnext */
 	HeapTupleData xs_ctup;		/* current heap tuple, if any */