diff --git a/src/interfaces/libpq/fe-trace.c b/src/interfaces/libpq/fe-trace.c
index ca59c183182..9a4595f5c87 100644
--- a/src/interfaces/libpq/fe-trace.c
+++ b/src/interfaces/libpq/fe-trace.c
@@ -40,8 +40,6 @@ PQtrace(PGconn *conn, FILE *debug_port)
 	if (debug_port == NULL)
 		return;
 
-	/* Make the trace stream line-buffered */
-	setvbuf(debug_port, NULL, _IOLBF, 0);
 	conn->Pfdebug = debug_port;
 	conn->traceFlags = 0;
 }
diff --git a/src/test/modules/libpq_pipeline/libpq_pipeline.c b/src/test/modules/libpq_pipeline/libpq_pipeline.c
index 081a84f8248..7aa78662653 100644
--- a/src/test/modules/libpq_pipeline/libpq_pipeline.c
+++ b/src/test/modules/libpq_pipeline/libpq_pipeline.c
@@ -1319,10 +1319,13 @@ main(int argc, char **argv)
 	/* Set the trace file, if requested */
 	if (tracefile != NULL)
 	{
-		trace = fopen(tracefile, "w+");
-
+		trace = fopen(tracefile, "w");
 		if (trace == NULL)
 			pg_fatal("could not open file \"%s\": %m", tracefile);
+
+		/* Make it line-buffered */
+		setvbuf(trace, NULL, _IOLBF, 0);
+
 		PQtrace(conn, trace);
 		PQtraceSetFlags(conn,
 						PQTRACE_SUPPRESS_TIMESTAMPS | PQTRACE_REGRESS_MODE);