diff --git a/src/backend/access/heap/tuptoaster.c b/src/backend/access/heap/tuptoaster.c
index 19e7048002..aa5a45ded4 100644
--- a/src/backend/access/heap/tuptoaster.c
+++ b/src/backend/access/heap/tuptoaster.c
@@ -1288,6 +1288,74 @@ toast_flatten_tuple_to_datum(HeapTupleHeader tup,
 }
 
 
+/* ----------
+ * toast_build_flattened_tuple -
+ *
+ *	Build a tuple containing no out-of-line toasted fields.
+ *	(This does not eliminate compressed or short-header datums.)
+ *
+ *	This is essentially just like heap_form_tuple, except that it will
+ *	expand any external-data pointers beforehand.
+ *
+ *	It's not very clear whether it would be preferable to decompress
+ *	in-line compressed datums while at it.  For now, we don't.
+ * ----------
+ */
+HeapTuple
+toast_build_flattened_tuple(TupleDesc tupleDesc,
+							Datum *values,
+							bool *isnull)
+{
+	HeapTuple	new_tuple;
+	Form_pg_attribute *att = tupleDesc->attrs;
+	int			numAttrs = tupleDesc->natts;
+	int			num_to_free;
+	int			i;
+	Datum		new_values[MaxTupleAttributeNumber];
+	Pointer		freeable_values[MaxTupleAttributeNumber];
+
+	/*
+	 * We can pass the caller's isnull array directly to heap_form_tuple, but
+	 * we potentially need to modify the values array.
+	 */
+	Assert(numAttrs <= MaxTupleAttributeNumber);
+	memcpy(new_values, values, numAttrs * sizeof(Datum));
+
+	num_to_free = 0;
+	for (i = 0; i < numAttrs; i++)
+	{
+		/*
+		 * Look at non-null varlena attributes
+		 */
+		if (!isnull[i] && att[i]->attlen == -1)
+		{
+			struct varlena *new_value;
+
+			new_value = (struct varlena *) DatumGetPointer(new_values[i]);
+			if (VARATT_IS_EXTERNAL(new_value))
+			{
+				new_value = heap_tuple_fetch_attr(new_value);
+				new_values[i] = PointerGetDatum(new_value);
+				freeable_values[num_to_free++] = (Pointer) new_value;
+			}
+		}
+	}
+
+	/*
+	 * Form the reconfigured tuple.
+	 */
+	new_tuple = heap_form_tuple(tupleDesc, new_values, isnull);
+
+	/*
+	 * Free allocated temp values
+	 */
+	for (i = 0; i < num_to_free; i++)
+		pfree(freeable_values[i]);
+
+	return new_tuple;
+}
+
+
 /* ----------
  * toast_compress_datum -
  *
diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index 02fb29cde3..982d16c6c8 100644
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -58,7 +58,7 @@
  */
 #include "postgres.h"
 
-#include "access/htup_details.h"
+#include "access/tuptoaster.h"
 #include "catalog/pg_type.h"
 #include "executor/execExpr.h"
 #include "executor/nodeSubplan.h"
@@ -3508,24 +3508,24 @@ ExecEvalWholeRowVar(ExprState *state, ExprEvalStep *op, ExprContext *econtext)
 	}
 
 	/*
-	 * Copy the slot tuple and make sure any toasted fields get detoasted.
+	 * Build a composite datum, making sure any toasted fields get detoasted.
 	 *
-	 * (The intermediate copy is a tad annoying here, but we currently have no
-	 * primitive that will do the right thing.  Note it is critical that we
-	 * not change the slot's state, so we can't use ExecFetchSlotTupleDatum.)
+	 * (Note: it is critical that we not change the slot's state here.)
 	 */
-	tuple = ExecCopySlotTuple(slot);
-	dtuple = (HeapTupleHeader)
-		DatumGetPointer(heap_copy_tuple_as_datum(tuple,
-												 slot->tts_tupleDescriptor));
-	heap_freetuple(tuple);
+	tuple = toast_build_flattened_tuple(slot->tts_tupleDescriptor,
+										slot->tts_values,
+										slot->tts_isnull);
+	dtuple = tuple->t_data;
 
 	/*
 	 * Label the datum with the composite type info we identified before.
+	 *
+	 * (Note: we could skip doing this by passing op->d.wholerow.tupdesc to
+	 * the tuple build step; but that seems a tad risky so let's not.)
 	 */
 	HeapTupleHeaderSetTypeId(dtuple, op->d.wholerow.tupdesc->tdtypeid);
 	HeapTupleHeaderSetTypMod(dtuple, op->d.wholerow.tupdesc->tdtypmod);
 
-	*op->resnull = false;
 	*op->resvalue = PointerGetDatum(dtuple);
+	*op->resnull = false;
 }
diff --git a/src/include/access/tuptoaster.h b/src/include/access/tuptoaster.h
index a6233c386d..c7abeed812 100644
--- a/src/include/access/tuptoaster.h
+++ b/src/include/access/tuptoaster.h
@@ -193,6 +193,17 @@ extern Datum toast_flatten_tuple_to_datum(HeapTupleHeader tup,
 							 uint32 tup_len,
 							 TupleDesc tupleDesc);
 
+/* ----------
+ * toast_build_flattened_tuple -
+ *
+ *	Build a tuple containing no out-of-line toasted fields.
+ *	(This does not eliminate compressed or short-header datums.)
+ * ----------
+ */
+extern HeapTuple toast_build_flattened_tuple(TupleDesc tupleDesc,
+							Datum *values,
+							bool *isnull);
+
 /* ----------
  * toast_compress_datum -
  *