diff --git a/usr.bin/uniq/tests/uniq_test.sh b/usr.bin/uniq/tests/uniq_test.sh
--- a/usr.bin/uniq/tests/uniq_test.sh
+++ b/usr.bin/uniq/tests/uniq_test.sh
@@ -119,6 +119,30 @@
 	atf_check_uniq --unique
 }
 
+atf_test_case interactive
+interactive_head() {
+	atf_set descr "test interactive use"
+}
+interactive_body() {
+	sh -c 'yes | stdbuf -oL uniq >actual' &
+	pid=$!
+	sleep 1
+	kill $!
+	atf_check -o inline:"y\n" cat actual
+}
+
+atf_test_case interactive_repeated
+interactive_repeated_head() {
+	atf_set descr "test interactive use with -d"
+}
+interactive_repeated_body() {
+	sh -c 'yes | stdbuf -oL uniq -d >actual' &
+	pid=$!
+	sleep 1
+	kill $!
+	atf_check -o inline:"y\n" cat actual
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case basic
@@ -131,4 +155,6 @@
 	atf_add_test_case ignore_case
 	atf_add_test_case skip_chars
 	atf_add_test_case unique
+	atf_add_test_case interactive
+	atf_add_test_case interactive_repeated
 }
diff --git a/usr.bin/uniq/uniq.c b/usr.bin/uniq/uniq.c
--- a/usr.bin/uniq/uniq.c
+++ b/usr.bin/uniq/uniq.c
@@ -140,6 +140,9 @@
 	if (argc > 2)
 		usage();
 
+	if (Dflag && dflag)
+		dflag = 0;
+
 	ifp = stdin;
 	ifn = "stdin";
 	ofp = stdout;
@@ -180,6 +183,8 @@
 			err(1, "%s", ifn);
 		exit(0);
 	}
+	if (!cflag && !Dflag && !dflag && !uflag)
+		show(ofp, prevline);
 	tprev = convert(prevline);
 
 	tthis = NULL;
@@ -199,7 +204,9 @@
 			/* If different, print; set previous to new value. */
 			if (Dflag == DF_POSTSEP && repeats > 0)
 				fputc('\n', ofp);
-			if (!Dflag)
+			if (!cflag && !Dflag && !dflag && !uflag)
+				show(ofp, thisline);
+			else if (!Dflag && !dflag)
 				show(ofp, prevline);
 			p = prevline;
 			b1 = prevbuflen;
@@ -220,13 +227,18 @@
 					show(ofp, prevline);
 				}
 				show(ofp, thisline);
+			} else if (dflag && !cflag) {
+				if (repeats == 0)
+					show(ofp, prevline);
 			}
 			++repeats;
 		}
 	}
 	if (ferror(ifp))
 		err(1, "%s", ifn);
-	if (!Dflag)
+	if (!cflag && !Dflag && !dflag && !uflag)
+		/* already printed */ ;
+	else if (!Dflag && (!dflag || cflag))
 		show(ofp, prevline);
 	exit(0);
 }
@@ -291,8 +303,7 @@
 static void
 show(FILE *ofp, const char *str)
 {
-
-	if ((!Dflag && dflag && repeats == 0) || (uflag && repeats > 0))
+	if (uflag && repeats > 0)
 		return;
 	if (cflag)
 		(void)fprintf(ofp, "%4d %s", repeats + 1, str);