diff --git a/usr.bin/ar/ar.c b/usr.bin/ar/ar.c
index 104d55ce85ca..4dee029b96aa 100644
--- a/usr.bin/ar/ar.c
+++ b/usr.bin/ar/ar.c
@@ -100,12 +100,12 @@ main(int argc, char **argv)
 	struct bsdar	*bsdar, bsdar_storage;
 	char		*p;
 	size_t		 len;
-	int		 i, opt;
+	int		 i, opt, Dflag, Uflag;
 
 	bsdar = &bsdar_storage;
 	memset(bsdar, 0, sizeof(*bsdar));
-	/* Enable deterministic mode by default. */
-	bsdar->options |= AR_D;
+	Dflag = 0;
+	Uflag = 0;
 
 	if ((bsdar->progname = getprogname()) == NULL)
 		bsdar->progname = "ar";
@@ -122,10 +122,12 @@ main(int argc, char **argv)
 				/* Ignored. */
 				break;
 			case 'D':
-				bsdar->options |= AR_D;
+				Dflag = 1;
+				Uflag = 0;
 				break;
 			case 'U':
-				bsdar->options &= ~AR_D;
+				Uflag = 1;
+				Dflag = 0;
 				break;
 			case 'V':
 				ranlib_version();
@@ -182,7 +184,8 @@ main(int argc, char **argv)
 			set_mode(bsdar, opt);
 			break;
 		case 'D':
-			bsdar->options |= AR_D;
+			Dflag = 1;
+			Uflag = 0;
 			break;
 		case 'f':
 		case 'T':
@@ -222,7 +225,8 @@ main(int argc, char **argv)
 			set_mode(bsdar, opt);
 			break;
 		case 'U':
-			bsdar->options &= ~AR_D;
+			Uflag = 1;
+			Dflag = 0;
 			break;
 		case 'u':
 			bsdar->options |= AR_U;
@@ -275,6 +279,10 @@ main(int argc, char **argv)
 		argv++;
 	}
 
+	/* Set determinstic mode for -D, and by default without -U. */
+	if (Dflag || (Uflag == 0 && (bsdar->mode == 'q' || bsdar->mode == 'r')))
+		bsdar->options |= AR_D;
+
 	if (bsdar->options & AR_A)
 		only_mode(bsdar, "-a", "mqr");
 	if (bsdar->options & AR_B)
@@ -283,8 +291,10 @@ main(int argc, char **argv)
 		only_mode(bsdar, "-c", "qr");
 	if (bsdar->options & AR_CC)
 		only_mode(bsdar, "-C", "x");
-	if (bsdar->options & AR_D)
+	if (Dflag)
 		only_mode(bsdar, "-D", "qr");
+	if (Uflag)
+		only_mode(bsdar, "-U", "qr");
 	if (bsdar->options & AR_O)
 		only_mode(bsdar, "-o", "x");
 	if (bsdar->options & AR_SS)