diff --git a/src/backend/postmaster/fork_process.c b/src/backend/postmaster/fork_process.c
index c75be03d2c..ec67761487 100644
--- a/src/backend/postmaster/fork_process.c
+++ b/src/backend/postmaster/fork_process.c
@@ -37,13 +37,8 @@ fork_process(void)
 
 	/*
 	 * Flush stdio channels just before fork, to avoid double-output problems.
-	 * Ideally we'd use fflush(NULL) here, but there are still a few non-ANSI
-	 * stdio libraries out there (like SunOS 4.1.x) that coredump if we do.
-	 * Presently stdout and stderr are the only stdio output channels used by
-	 * the postmaster, so fflush'ing them should be sufficient.
 	 */
-	fflush(stdout);
-	fflush(stderr);
+	fflush(NULL);
 
 #ifdef LINUX_PROFILE
 
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index e3b19ca1ed..1aaab6c554 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -2503,8 +2503,7 @@ OpenPipeStream(const char *command, const char *mode)
 	ReleaseLruFiles();
 
 TryAgain:
-	fflush(stdout);
-	fflush(stderr);
+	fflush(NULL);
 	pqsignal(SIGPIPE, SIG_DFL);
 	errno = 0;
 	file = popen(command, mode);
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 95f32de4e2..cb3c289889 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -643,8 +643,7 @@ errfinish(const char *filename, int lineno, const char *funcname)
 		 * Any other code you might be tempted to add here should probably be
 		 * in an on_proc_exit or on_shmem_exit callback instead.
 		 */
-		fflush(stdout);
-		fflush(stderr);
+		fflush(NULL);
 
 		/*
 		 * Let the cumulative stats system know. Only mark the session as
@@ -670,8 +669,7 @@ errfinish(const char *filename, int lineno, const char *funcname)
 		 * XXX: what if we are *in* the postmaster?  abort() won't kill our
 		 * children...
 		 */
-		fflush(stdout);
-		fflush(stderr);
+		fflush(NULL);
 		abort();
 	}
 
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 29c28b7315..8567c875fe 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -489,8 +489,7 @@ popen_check(const char *command, const char *mode)
 {
 	FILE	   *cmdfd;
 
-	fflush(stdout);
-	fflush(stderr);
+	fflush(NULL);
 	errno = 0;
 	cmdfd = popen(command, mode);
 	if (cmdfd == NULL)
diff --git a/src/bin/pg_ctl/pg_ctl.c b/src/bin/pg_ctl/pg_ctl.c
index 73e20081d1..be2af9f261 100644
--- a/src/bin/pg_ctl/pg_ctl.c
+++ b/src/bin/pg_ctl/pg_ctl.c
@@ -448,8 +448,7 @@ start_postmaster(void)
 	pgpid_t		pm_pid;
 
 	/* Flush stdio channels just before fork, to avoid double-output problems */
-	fflush(stdout);
-	fflush(stderr);
+	fflush(NULL);
 
 #ifdef EXEC_BACKEND
 	pg_disable_aslr();
diff --git a/src/bin/pg_dump/pg_dumpall.c b/src/bin/pg_dump/pg_dumpall.c
index 68c455f84b..d665b257c9 100644
--- a/src/bin/pg_dump/pg_dumpall.c
+++ b/src/bin/pg_dump/pg_dumpall.c
@@ -1578,8 +1578,7 @@ runPgDump(const char *dbname, const char *create_opts)
 
 	pg_log_info("running \"%s\"", cmd->data);
 
-	fflush(stdout);
-	fflush(stderr);
+	fflush(NULL);
 
 	ret = system(cmd->data);
 
diff --git a/src/bin/pg_upgrade/controldata.c b/src/bin/pg_upgrade/controldata.c
index e2086a07de..018cd310f7 100644
--- a/src/bin/pg_upgrade/controldata.c
+++ b/src/bin/pg_upgrade/controldata.c
@@ -123,8 +123,7 @@ get_control_data(ClusterInfo *cluster, bool live_check)
 		/* only pg_controldata outputs the cluster state */
 		snprintf(cmd, sizeof(cmd), "\"%s/pg_controldata\" \"%s\"",
 				 cluster->bindir, cluster->pgdata);
-		fflush(stdout);
-		fflush(stderr);
+		fflush(NULL);
 
 		if ((output = popen(cmd, "r")) == NULL)
 			pg_fatal("could not get control data using %s: %s",
@@ -191,8 +190,7 @@ get_control_data(ClusterInfo *cluster, bool live_check)
 			 cluster->bindir,
 			 live_check ? "pg_controldata\"" : resetwal_bin,
 			 cluster->pgdata);
-	fflush(stdout);
-	fflush(stderr);
+	fflush(NULL);
 
 	if ((output = popen(cmd, "r")) == NULL)
 		pg_fatal("could not get control data using %s: %s",
diff --git a/src/bin/psql/copy.c b/src/bin/psql/copy.c
index c181682a13..0f66ebc2ed 100644
--- a/src/bin/psql/copy.c
+++ b/src/bin/psql/copy.c
@@ -288,8 +288,7 @@ do_copy(const char *args)
 		{
 			if (options->program)
 			{
-				fflush(stdout);
-				fflush(stderr);
+				fflush(NULL);
 				errno = 0;
 				copystream = popen(options->file, PG_BINARY_R);
 			}
@@ -307,10 +306,9 @@ do_copy(const char *args)
 		{
 			if (options->program)
 			{
-				fflush(stdout);
-				fflush(stderr);
-				errno = 0;
+				fflush(NULL);
 				disable_sigpipe_trap();
+				errno = 0;
 				copystream = popen(options->file, PG_BINARY_W);
 			}
 			else
diff --git a/src/common/exec.c b/src/common/exec.c
index fdcad0ee8c..81ff86dce6 100644
--- a/src/common/exec.c
+++ b/src/common/exec.c
@@ -389,8 +389,7 @@ pipe_read_line(char *cmd, char *line, int maxsize)
 	FILE	   *pgver;
 
 	/* flush output buffers in case popen does not... */
-	fflush(stdout);
-	fflush(stderr);
+	fflush(NULL);
 
 	errno = 0;
 	if ((pgver = popen(cmd, "r")) == NULL)
diff --git a/src/test/regress/pg_regress.c b/src/test/regress/pg_regress.c
index a803355f8e..3c92aa8836 100644
--- a/src/test/regress/pg_regress.c
+++ b/src/test/regress/pg_regress.c
@@ -264,8 +264,7 @@ stop_postmaster(void)
 		int			r;
 
 		/* On Windows, system() seems not to force fflush, so... */
-		fflush(stdout);
-		fflush(stderr);
+		fflush(NULL);
 
 		snprintf(buf, sizeof(buf),
 				 "\"%s%spg_ctl\" stop -D \"%s/data\" -s",
@@ -1063,13 +1062,9 @@ spawn_process(const char *cmdline)
 	pid_t		pid;
 
 	/*
-	 * Must flush I/O buffers before fork.  Ideally we'd use fflush(NULL) here
-	 * ... does anyone still care about systems where that doesn't work?
+	 * Must flush I/O buffers before fork.
 	 */
-	fflush(stdout);
-	fflush(stderr);
-	if (logfile)
-		fflush(logfile);
+	fflush(NULL);
 
 #ifdef EXEC_BACKEND
 	pg_disable_aslr();