fix `assert()` crash (#1941)

2 files changed, 9 insertions, 1 deletions

diff --git a/src/string_immutable.zig b/src/string_immutable.zig
index a437baa69..e949892e1 100644
--- a/src/string_immutable.zig
+++ b/src/string_immutable.zig
@@ -1419,7 +1419,7 @@ pub fn convertUTF8BytesIntoUTF16(sequence: *const [4]u8) UTF16Replacement {
     switch (len) {
         2 => {
             if (Environment.allow_assert)
-                assert(sequence[0] >= 0xC2);
+                assert(sequence[0] >= 0xC0);
             if (Environment.allow_assert)
                 assert(sequence[0] <= 0xDF);
             if (sequence[1] < 0x80 or sequence[1] > 0xBF) {
diff --git a/test/bun.js/buffer.test.js b/test/bun.js/buffer.test.js
index 1971fed8c..d1ed5a496 100644
--- a/test/bun.js/buffer.test.js
+++ b/test/bun.js/buffer.test.js
@@ -2813,3 +2813,11 @@ test("Buffer.byteLength", () => {
     );
   }
 });
+
+it("should not crash on invalid UTF-8 byte sequence", () => {
+  const buf = Buffer.from([0xC0, 0xFD]).toString();
+  expect(buf.length).toBe(2);
+  const str = buf.toString();
+  expect(str.length).toBe(2);
+  expect(str).toBe("\uFFFD\uFFFD");
+});