diff --git a/usr.bin/ar/ar.1 b/usr.bin/ar/ar.1
index 02e99f1a92c9..6998c04e0d9c 100644
--- a/usr.bin/ar/ar.1
+++ b/usr.bin/ar/ar.1
@@ -210,6 +210,7 @@ and 0644 instead of file mode from the members named by arguments
 .Ar .
 This ensures that checksums on the resulting archives are reproducible
 when member contents are identical.
+This option is enabled by default.
 If multiple
 .Fl D
 and
diff --git a/usr.bin/ar/ar.c b/usr.bin/ar/ar.c
index 3d5e2b87667b..104d55ce85ca 100644
--- a/usr.bin/ar/ar.c
+++ b/usr.bin/ar/ar.c
@@ -104,6 +104,8 @@ main(int argc, char **argv)
 
 	bsdar = &bsdar_storage;
 	memset(bsdar, 0, sizeof(*bsdar));
+	/* Enable deterministic mode by default. */
+	bsdar->options |= AR_D;
 
 	if ((bsdar->progname = getprogname()) == NULL)
 		bsdar->progname = "ar";