diff --git a/coreutils/sort.c b/coreutils/sort.c
index 80b578fc2..01b7c44e5 100644
--- a/coreutils/sort.c
+++ b/coreutils/sort.c
@@ -652,11 +652,12 @@ int sort_main(int argc UNUSED_PARAM, char **argv)
 	/* Handle -u */
 	if (option_mask32 & FLAG_u) {
 		int j = 0;
-		/* coreutils 6.3 drop lines for which only key is the same
-		 * -- disabling last-resort compare, or else compare_keys()
-		 * will be the same only for completely identical lines.
+		/* coreutils 6.3 drop lines for which only key is the same:
+		 * - disabling last-resort compare, or else compare_keys()
+		 * will be the same only for completely identical lines
+		 * - disabling -s (same reasons)
 		 */
-		option_mask32 |= FLAG_no_tie_break;
+		option_mask32 = (option_mask32 | FLAG_no_tie_break) & (~FLAG_s);
 		for (i = 1; i < linecount; i++) {
 			if (compare_keys(&lines[j], &lines[i]) == 0)
 				free(lines[i]);
diff --git a/testsuite/sort.tests b/testsuite/sort.tests
index fb2cc91bd..8dbadbdae 100755
--- a/testsuite/sort.tests
+++ b/testsuite/sort.tests
@@ -230,4 +230,14 @@ testing "sort -k2,2M" \
 3 March
 " ""
 
+testing "sort -s -u" \
+"sort -s -u -k 2 input" "\
+z a
+z b
+" "\
+z b
+a b
+z a
+a a" ""
+
 exit $FAILCOUNT