diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 9854b51c6a..1da3b8eb2e 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -171,10 +171,10 @@ const struct config_enum_entry sync_method_options[] = {
 #ifdef HAVE_FDATASYNC
 	{"fdatasync", SYNC_METHOD_FDATASYNC, false},
 #endif
-#ifdef OPEN_SYNC_FLAG
+#ifdef O_SYNC
 	{"open_sync", SYNC_METHOD_OPEN, false},
 #endif
-#ifdef OPEN_DATASYNC_FLAG
+#ifdef O_DSYNC
 	{"open_datasync", SYNC_METHOD_OPEN_DSYNC, false},
 #endif
 	{NULL, 0, false}
@@ -7894,10 +7894,10 @@ get_sync_bit(int method)
 
 	/*
 	 * Optimize writes by bypassing kernel cache with O_DIRECT when using
-	 * O_SYNC/O_FSYNC and O_DSYNC.  But only if archiving and streaming are
-	 * disabled, otherwise the archive command or walsender process will read
-	 * the WAL soon after writing it, which is guaranteed to cause a physical
-	 * read if we bypassed the kernel cache. We also skip the
+	 * O_SYNC and O_DSYNC.  But only if archiving and streaming are disabled,
+	 * otherwise the archive command or walsender process will read the WAL
+	 * soon after writing it, which is guaranteed to cause a physical read if
+	 * we bypassed the kernel cache. We also skip the
 	 * posix_fadvise(POSIX_FADV_DONTNEED) call in XLogFileClose() for the same
 	 * reason.
 	 *
@@ -7921,13 +7921,13 @@ get_sync_bit(int method)
 		case SYNC_METHOD_FSYNC_WRITETHROUGH:
 		case SYNC_METHOD_FDATASYNC:
 			return 0;
-#ifdef OPEN_SYNC_FLAG
+#ifdef O_SYNC
 		case SYNC_METHOD_OPEN:
-			return OPEN_SYNC_FLAG | o_direct_flag;
+			return O_SYNC | o_direct_flag;
 #endif
-#ifdef OPEN_DATASYNC_FLAG
+#ifdef O_DSYNC
 		case SYNC_METHOD_OPEN_DSYNC:
-			return OPEN_DATASYNC_FLAG | o_direct_flag;
+			return O_DSYNC | o_direct_flag;
 #endif
 		default:
 			/* can't happen (unless we are out of sync with option array) */
diff --git a/src/bin/pg_test_fsync/pg_test_fsync.c b/src/bin/pg_test_fsync/pg_test_fsync.c
index f7bc199a30..6739214eb8 100644
--- a/src/bin/pg_test_fsync/pg_test_fsync.c
+++ b/src/bin/pg_test_fsync/pg_test_fsync.c
@@ -300,7 +300,7 @@ test_sync(int writes_per_op)
 	printf(LABEL_FORMAT, "open_datasync");
 	fflush(stdout);
 
-#ifdef OPEN_DATASYNC_FLAG
+#ifdef O_DSYNC
 	if ((tmpfile = open_direct(filename, O_RDWR | O_DSYNC | PG_BINARY, 0)) == -1)
 	{
 		printf(NA_FORMAT, _("n/a*"));
@@ -407,8 +407,8 @@ test_sync(int writes_per_op)
 	printf(LABEL_FORMAT, "open_sync");
 	fflush(stdout);
 
-#ifdef OPEN_SYNC_FLAG
-	if ((tmpfile = open_direct(filename, O_RDWR | OPEN_SYNC_FLAG | PG_BINARY, 0)) == -1)
+#ifdef O_SYNC
+	if ((tmpfile = open_direct(filename, O_RDWR | O_SYNC | PG_BINARY, 0)) == -1)
 	{
 		printf(NA_FORMAT, _("n/a*"));
 		fs_warning = true;
@@ -466,7 +466,7 @@ test_open_syncs(void)
 static void
 test_open_sync(const char *msg, int writes_size)
 {
-#ifdef OPEN_SYNC_FLAG
+#ifdef O_SYNC
 	int			tmpfile,
 				ops,
 				writes;
@@ -475,8 +475,8 @@ test_open_sync(const char *msg, int writes_size)
 	printf(LABEL_FORMAT, msg);
 	fflush(stdout);
 
-#ifdef OPEN_SYNC_FLAG
-	if ((tmpfile = open_direct(filename, O_RDWR | OPEN_SYNC_FLAG | PG_BINARY, 0)) == -1)
+#ifdef O_SYNC
+	if ((tmpfile = open_direct(filename, O_RDWR | O_SYNC | PG_BINARY, 0)) == -1)
 		printf(NA_FORMAT, _("n/a*"));
 	else
 	{
diff --git a/src/include/access/xlogdefs.h b/src/include/access/xlogdefs.h
index a47e3eeb1f..810cd1fd86 100644
--- a/src/include/access/xlogdefs.h
+++ b/src/include/access/xlogdefs.h
@@ -69,28 +69,12 @@ typedef uint16 RepOriginId;
  * are available on the current platform, and to choose an appropriate
  * default method.  We assume that fsync() is always available, and that
  * configure determined whether fdatasync() is.
+ *
+ * Note that we define our own O_DSYNC on Windows, but not O_SYNC.
  */
-#if defined(O_SYNC)
-#define OPEN_SYNC_FLAG		O_SYNC
-#elif defined(O_FSYNC)
-#define OPEN_SYNC_FLAG		O_FSYNC
-#endif
-
-#if defined(O_DSYNC)
-#if defined(OPEN_SYNC_FLAG)
-/* O_DSYNC is distinct? */
-#if O_DSYNC != OPEN_SYNC_FLAG
-#define OPEN_DATASYNC_FLAG		O_DSYNC
-#endif
-#else							/* !defined(OPEN_SYNC_FLAG) */
-/* Win32 only has O_DSYNC */
-#define OPEN_DATASYNC_FLAG		O_DSYNC
-#endif
-#endif
-
 #if defined(PLATFORM_DEFAULT_SYNC_METHOD)
 #define DEFAULT_SYNC_METHOD		PLATFORM_DEFAULT_SYNC_METHOD
-#elif defined(OPEN_DATASYNC_FLAG)
+#elif defined(O_DSYNC) && (!defined(O_SYNC) || O_DSYNC != O_SYNC)
 #define DEFAULT_SYNC_METHOD		SYNC_METHOD_OPEN_DSYNC
 #elif defined(HAVE_FDATASYNC)
 #define DEFAULT_SYNC_METHOD		SYNC_METHOD_FDATASYNC