diff --git a/src/interfaces/libpq/fe-trace.c b/src/interfaces/libpq/fe-trace.c
index 51b01fd40e5..61a7e489671 100644
--- a/src/interfaces/libpq/fe-trace.c
+++ b/src/interfaces/libpq/fe-trace.c
@@ -549,7 +549,16 @@ pqTraceOutputMessage(PGconn *conn, const char *message, bool toServer)
 	length = (int) pg_ntoh32(length);
 	logCursor += 4;
 
-	fprintf(conn->Pfdebug, "%s\t%d\t", prefix, length);
+	/*
+	 * In regress mode, suppress the length of ErrorResponse and
+	 * NoticeResponse.  The F (file name), L (line number) and R (routine
+	 * name) fields can change as server code is modified, and if their
+	 * lengths differ from the originals, that would break tests.
+	 */
+	if (regress && !toServer && (id == 'E' || id == 'N'))
+		fprintf(conn->Pfdebug, "%s\tNN\t", prefix);
+	else
+		fprintf(conn->Pfdebug, "%s\t%d\t", prefix, length);
 
 	switch (id)
 	{
diff --git a/src/test/modules/libpq_pipeline/traces/pipeline_abort.trace b/src/test/modules/libpq_pipeline/traces/pipeline_abort.trace
index b0614357856..254e4859975 100644
--- a/src/test/modules/libpq_pipeline/traces/pipeline_abort.trace
+++ b/src/test/modules/libpq_pipeline/traces/pipeline_abort.trace
@@ -1,5 +1,5 @@
 F	42	Query	 "DROP TABLE IF EXISTS pq_pipeline_demo"
-B	123	NoticeResponse	 S "NOTICE" V "NOTICE" C "00000" M "table "pq_pipeline_demo" does not exist, skipping" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	NoticeResponse	 S "NOTICE" V "NOTICE" C "00000" M "table "pq_pipeline_demo" does not exist, skipping" F "SSSS" L "SSSS" R "SSSS" \x00
 B	15	CommandComplete	 "DROP TABLE"
 B	5	ReadyForQuery	 I
 F	99	Query	 "CREATE UNLOGGED TABLE pq_pipeline_demo(id serial primary key, itemno integer,int8filler int8);"
@@ -27,7 +27,7 @@ B	4	ParseComplete
 B	4	BindComplete
 B	4	NoData
 B	15	CommandComplete	 "INSERT 0 1"
-B	217	ErrorResponse	 S "ERROR" V "ERROR" C "42883" M "function no_such_function(integer) does not exist" H "No function matches the given name and argument types. You might need to add explicit type casts." P "8" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	ErrorResponse	 S "ERROR" V "ERROR" C "42883" M "function no_such_function(integer) does not exist" H "No function matches the given name and argument types. You might need to add explicit type casts." P "8" F "SSSS" L "SSSS" R "SSSS" \x00
 B	5	ReadyForQuery	 I
 B	4	ParseComplete
 B	4	BindComplete
@@ -39,7 +39,7 @@ F	12	Bind	 "" "" 0 0 0
 F	6	Describe	 P ""
 F	9	Execute	 "" 0
 F	4	Sync
-B	123	ErrorResponse	 S "ERROR" V "ERROR" C "42601" M "cannot insert multiple commands into a prepared statement" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	ErrorResponse	 S "ERROR" V "ERROR" C "42601" M "cannot insert multiple commands into a prepared statement" F "SSSS" L "SSSS" R "SSSS" \x00
 B	5	ReadyForQuery	 I
 F	54	Parse	 "" "SELECT 1.0/g FROM generate_series(3, -1, -1) g" 0
 F	12	Bind	 "" "" 0 0 0
@@ -52,7 +52,7 @@ B	33	RowDescription	 1 "?column?" NNNN 0 NNNN 65535 -1 0
 B	32	DataRow	 1 22 '0.33333333333333333333'
 B	32	DataRow	 1 22 '0.50000000000000000000'
 B	32	DataRow	 1 22 '1.00000000000000000000'
-B	70	ErrorResponse	 S "ERROR" V "ERROR" C "22012" M "division by zero" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	ErrorResponse	 S "ERROR" V "ERROR" C "22012" M "division by zero" F "SSSS" L "SSSS" R "SSSS" \x00
 B	5	ReadyForQuery	 I
 F	40	Query	 "SELECT itemno FROM pq_pipeline_demo"
 B	31	RowDescription	 1 "itemno" NNNN 2 NNNN 4 -1 0
diff --git a/src/test/modules/libpq_pipeline/traces/transaction.trace b/src/test/modules/libpq_pipeline/traces/transaction.trace
index 0267a534fa1..1dcc2373c0b 100644
--- a/src/test/modules/libpq_pipeline/traces/transaction.trace
+++ b/src/test/modules/libpq_pipeline/traces/transaction.trace
@@ -1,5 +1,5 @@
 F	79	Query	 "DROP TABLE IF EXISTS pq_pipeline_tst;CREATE TABLE pq_pipeline_tst (id int)"
-B	122	NoticeResponse	 S "NOTICE" V "NOTICE" C "00000" M "table "pq_pipeline_tst" does not exist, skipping" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	NoticeResponse	 S "NOTICE" V "NOTICE" C "00000" M "table "pq_pipeline_tst" does not exist, skipping" F "SSSS" L "SSSS" R "SSSS" \x00
 B	15	CommandComplete	 "DROP TABLE"
 B	17	CommandComplete	 "CREATE TABLE"
 B	5	ReadyForQuery	 I
@@ -40,9 +40,9 @@ B	4	BindComplete
 B	4	NoData
 B	10	CommandComplete	 "BEGIN"
 B	4	ParseComplete
-B	65	ErrorResponse	 S "ERROR" V "ERROR" C "22012" M "division by zero" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	ErrorResponse	 S "ERROR" V "ERROR" C "22012" M "division by zero" F "SSSS" L "SSSS" R "SSSS" \x00
 B	5	ReadyForQuery	 E
-B	145	ErrorResponse	 S "ERROR" V "ERROR" C "25P02" M "current transaction is aborted, commands ignored until end of transaction block" F "SSSS" L "SSSS" R "SSSS" \x00
+B	NN	ErrorResponse	 S "ERROR" V "ERROR" C "25P02" M "current transaction is aborted, commands ignored until end of transaction block" F "SSSS" L "SSSS" R "SSSS" \x00
 B	5	ReadyForQuery	 E
 B	4	BindComplete
 B	4	NoData