diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c
index 5850608a3fb..a187d8ec284 100644
--- a/src/backend/commands/copyto.c
+++ b/src/backend/commands/copyto.c
@@ -395,22 +395,38 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot)
 	else
 	{
 		/*
-		 * Full table or query without column list.  For queries, the slot's
-		 * TupleDesc may carry RECORDOID, which is not registered in the type
-		 * cache and would cause composite_to_json's lookup_rowtype_tupdesc
-		 * call to fail.  Build a HeapTuple stamped with the blessed
-		 * descriptor so the type can be looked up correctly.
+		 * Full table or query without column list.  For a query, the slot's
+		 * descriptor is either an unregistered RECORD type, which
+		 * composite_to_json's lookup_rowtype_tupdesc() cannot look up, or,
+		 * when the top plan node does not project, the row type of a scanned
+		 * table, whose column names need not match the query's.  Either way,
+		 * the datum must be stamped with the query's blessed descriptor.
+		 *
+		 * A virtual slot has no physical tuple, so form one directly.
+		 * Otherwise copy the slot's tuple and stamp the copy with the query's
+		 * descriptor.  That is safe because the tuple's physical layout
+		 * matches the query's result descriptor: a scan returns its scan
+		 * tuple unprojected only if tlist_matches_tupdesc() holds, which
+		 * rules out dropped columns and columns with missing values.
 		 */
-		if (!cstate->rel && slot->tts_tupleDescriptor->tdtypeid == RECORDOID)
-		{
-			HeapTuple	tup = heap_form_tuple(cstate->tupDesc,
-											  slot->tts_values,
-											  slot->tts_isnull);
-
-			rowdata = HeapTupleGetDatum(tup);
-		}
-		else
+		if (cstate->rel)
 			rowdata = ExecFetchSlotHeapTupleDatum(slot);
+		else if (TTS_IS_VIRTUAL(slot))
+			rowdata = HeapTupleGetDatum(heap_form_tuple(cstate->tupDesc,
+														slot->tts_values,
+														slot->tts_isnull));
+		else
+		{
+			HeapTuple	tup;
+			bool		shouldFree;
+
+			Assert(slot->tts_tupleDescriptor->natts == cstate->tupDesc->natts);
+
+			tup = ExecFetchSlotHeapTuple(slot, false, &shouldFree);
+			rowdata = heap_copy_tuple_as_datum(tup, cstate->tupDesc);
+			if (shouldFree)
+				heap_freetuple(tup);
+		}
 	}
 
 	composite_to_json(rowdata, cstate->json_buf, false);
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
index 0af0b646921..979bef5f3f2 100644
--- a/src/test/regress/expected/copy.out
+++ b/src/test/regress/expected/copy.out
@@ -117,6 +117,19 @@ copy (select * from copytest) to stdout (format json);
 {"style":"Unix","test":"abc\ndef","filler":2}
 {"style":"Mac","test":"abc\rdef","filler":3}
 {"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4}
+-- keys are the query's column names, also when a scan does not project
+copy (select a as x, b as y, c as z from copytest_order) to stdout (format json);
+{"x":1,"y":2,"z":3}
+create temp table copytest_order2 (c int, b int, a int);
+insert into copytest_order2 values (4, 5, 6);
+copy (select * from copytest_order union all select * from copytest_order2)
+  to stdout (format json);
+{"a":1,"b":2,"c":3}
+{"a":4,"b":5,"c":6}
+-- columns with missing values force a projection
+alter table copytest_order2 add column d int default 7;
+copy (select * from copytest_order2) to stdout (format json);
+{"c":4,"b":5,"a":6,"d":7}
 -- all of the following should yield error
 copy copytest to stdout (format json, delimiter '|');
 ERROR:  cannot specify DELIMITER in JSON mode
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
index 14da3c5ec37..6d3923fb3f0 100644
--- a/src/test/regress/sql/copy.sql
+++ b/src/test/regress/sql/copy.sql
@@ -101,6 +101,16 @@ copy copytest to stdout json;
 copy copytest to stdout (format json);
 copy (select * from copytest) to stdout (format json);
 
+-- keys are the query's column names, also when a scan does not project
+copy (select a as x, b as y, c as z from copytest_order) to stdout (format json);
+create temp table copytest_order2 (c int, b int, a int);
+insert into copytest_order2 values (4, 5, 6);
+copy (select * from copytest_order union all select * from copytest_order2)
+  to stdout (format json);
+-- columns with missing values force a projection
+alter table copytest_order2 add column d int default 7;
+copy (select * from copytest_order2) to stdout (format json);
+
 -- all of the following should yield error
 copy copytest to stdout (format json, delimiter '|');
 copy copytest to stdout (format json, null '\N');