diff --git a/src/test/regress/expected/failure_copy_on_hash.out b/src/test/regress/expected/failure_copy_on_hash.out
index 424ab0da85d..35cb690c866 100644
--- a/src/test/regress/expected/failure_copy_on_hash.out
+++ b/src/test/regress/expected/failure_copy_on_hash.out
@@ -270,7 +270,9 @@ SELECT citus.mitmproxy('conn.kill()');
 
 (1 row)
 
-\COPY test_table_2 FROM stdin delimiter ',';
+-- Deliberately use zero-row input; modern psql drains failed COPY input
+-- through the next \. (#8780).
+\COPY test_table_2 FROM PROGRAM 'true' delimiter ',';
 ERROR:  connection to the remote node postgres@localhost:xxxxx failed with the following error: connection not open
 SELECT citus.mitmproxy('conn.allow()');
  mitmproxy
diff --git a/src/test/regress/expected/failure_copy_to_reference.out b/src/test/regress/expected/failure_copy_to_reference.out
index 8c610572edb..12bfd1fe21f 100644
--- a/src/test/regress/expected/failure_copy_to_reference.out
+++ b/src/test/regress/expected/failure_copy_to_reference.out
@@ -34,7 +34,9 @@ SELECT citus.mitmproxy('conn.kill()');
 
 (1 row)
 
-\copy test_table FROM STDIN DELIMITER ','
+-- Deliberately use zero-row input for the next three failures; modern psql
+-- drains failed COPY input through the next \. (#8780).
+\copy test_table FROM PROGRAM 'true' DELIMITER ','
 ERROR:  failure on connection marked as essential: localhost:xxxxx
 SELECT citus.mitmproxy('conn.allow()');
  mitmproxy
@@ -61,7 +63,7 @@ SELECT citus.mitmproxy('conn.onQuery(query="^BEGIN TRANSACTION ISOLATION LEVEL R
 
 (1 row)
 
-\copy test_table FROM STDIN DELIMITER ','
+\copy test_table FROM PROGRAM 'true' DELIMITER ','
 ERROR:  failure on connection marked as essential: localhost:xxxxx
 SELECT citus.mitmproxy('conn.allow()');
  mitmproxy
@@ -88,7 +90,7 @@ SELECT citus.mitmproxy('conn.onQuery(query="^BEGIN TRANSACTION ISOLATION LEVEL R
 
 (1 row)
 
-\copy test_table FROM STDIN DELIMITER ','
+\copy test_table FROM PROGRAM 'true' DELIMITER ','
 ERROR:  canceling statement due to user request
 SELECT citus.mitmproxy('conn.allow()');
  mitmproxy
diff --git a/src/test/regress/sql/failure_copy_on_hash.sql b/src/test/regress/sql/failure_copy_on_hash.sql
index d60242803c4..91e18b42bf0 100644
--- a/src/test/regress/sql/failure_copy_on_hash.sql
+++ b/src/test/regress/sql/failure_copy_on_hash.sql
@@ -141,7 +141,9 @@ SELECT create_distributed_table('test_table_2','id');
 
 SELECT citus.mitmproxy('conn.kill()');
 
-\COPY test_table_2 FROM stdin delimiter ',';
+-- Deliberately use zero-row input; modern psql drains failed COPY input
+-- through the next \. (#8780).
+\COPY test_table_2 FROM PROGRAM 'true' delimiter ',';
 
 SELECT citus.mitmproxy('conn.allow()');
 SELECT pds.logicalrelid, pdsd.shardid, pdsd.shardstate
diff --git a/src/test/regress/sql/failure_copy_to_reference.sql b/src/test/regress/sql/failure_copy_to_reference.sql
index b6c8d6c81aa..3e686ab5fc8 100644
--- a/src/test/regress/sql/failure_copy_to_reference.sql
+++ b/src/test/regress/sql/failure_copy_to_reference.sql
@@ -24,21 +24,23 @@ CREATE VIEW unhealthy_shard_count AS
 -- in the first test, kill just in the first
 -- response we get from the worker
 SELECT citus.mitmproxy('conn.kill()');
-\copy test_table FROM STDIN DELIMITER ','
+-- Deliberately use zero-row input for the next three failures; modern psql
+-- drains failed COPY input through the next \. (#8780).
+\copy test_table FROM PROGRAM 'true' DELIMITER ','
 SELECT citus.mitmproxy('conn.allow()');
 SELECT * FROM unhealthy_shard_count;
 SELECT count(*) FROM test_table;
 
 -- kill as soon as the coordinator sends begin
 SELECT citus.mitmproxy('conn.onQuery(query="^BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED").kill()');
-\copy test_table FROM STDIN DELIMITER ','
+\copy test_table FROM PROGRAM 'true' DELIMITER ','
 SELECT citus.mitmproxy('conn.allow()');
 SELECT * FROM unhealthy_shard_count;
 SELECT count(*) FROM test_table;
 
 -- cancel as soon as the coordinator sends begin
 SELECT citus.mitmproxy('conn.onQuery(query="^BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED").cancel(' ||  pg_backend_pid() || ')');
-\copy test_table FROM STDIN DELIMITER ','
+\copy test_table FROM PROGRAM 'true' DELIMITER ','
 SELECT citus.mitmproxy('conn.allow()');
 SELECT * FROM unhealthy_shard_count;
 SELECT count(*) FROM test_table;