diff --git a/src/htsback.c b/src/htsback.c
index e1a9bf962..610726774 100644
--- a/src/htsback.c
+++ b/src/htsback.c
@@ -4094,13 +4094,25 @@ void back_wait(struct_back * sback, httrackp * opt, cache_back * cache,
                   int noFreebuff = 0;
                   LLint content_length = -1;
                   hts_boolean length_conflict = HTS_FALSE;
+                  /* binput_line stops at a NUL, hiding the fields after it */
+                  const hts_boolean has_nul =
+                      back[i].r.adr[0] != '<' &&
+                      memchr(back[i].r.adr, '\0', (size_t) back[i].r.size) !=
+                          NULL;
 
-                  /* Hack for zero-length headers */
-                  if (back_status(&back[i]) != 0 && back[i].r.adr[0] != '<') {
-
+                  if (has_nul) {
+                    hts_log_print(opt, LOG_WARNING,
+                                  "NUL byte in response header, response "
+                                  "dropped: %s%s",
+                                  adr_nologin(opt, back[i].url_adr),
+                                  back[i].url_fil);
+                    back_slot_close_fail(opt, sback, i, STATUSCODE_INVALID,
+                                         "NUL byte in response header");
+                  } else if (back_status(&back[i]) != 0 &&
+                             back[i].r.adr[0] != '<') {
+                    /* Hack for zero-length headers */
                     // ----------------------------------------
-                    // traiter en-tête!
-                    // status-line à récupérer
+                    /* parse the header, status line first */
                     binput_line(back[i].r.adr + ptr,
                                 back[i].r.adr + back[i].r.size, rcvd, 2000,
                                 &adv);
@@ -4202,7 +4214,8 @@ void back_wait(struct_back * sback, httrackp * opt, cache_back * cache,
                                   back[i].url_fil);
                     back_slot_close_fail(opt, sback, i, STATUSCODE_INVALID,
                                          "Conflicting Content-Length");
-                  } else {
+                  } else if (!has_nul) {
+                    /* a plugin must not see the header of a dropped response */
                     int test_head = RUN_CALLBACK6(opt, receivehead,
                                                   back[i].r.adr,
                                                   back[i].url_adr,
diff --git a/tests/2311_local-header-nul.test b/tests/2311_local-header-nul.test
new file mode 100755
index 000000000..e3c95c415
--- /dev/null
+++ b/tests/2311_local-header-nul.test
@@ -0,0 +1,22 @@
+#!/bin/bash
+#
+# RFC 9110 5.5: a NUL byte in a response header drops the response.
+
+set -euo pipefail
+
+: "${top_srcdir:=..}"
+
+bash "$top_srcdir/tests/local-crawl.sh" \
+    --file-bytes 'nulhdr/clean.bin' 16 \
+    --file-bytes 'nulhdr/body-nul.bin' 16 \
+    --file-matches 'nulhdr/bare.html' 'bare-ok' \
+    --file-matches '../cookies.txt' 'good' \
+    --file-not-matches '../cookies.txt' 'nulcookie' \
+    --not-found 'nulhdr/in-list.bin' --not-found 'nulhdr/ends-block.bin' \
+    --not-found 'nulhdr/cookie.bin' --not-found 'nulhdr/status.bin' \
+    --log-found 'NUL byte in response header, response dropped: .*/nulhdr/in-list\.bin' \
+    --log-found 'NUL byte in response header, response dropped: .*/nulhdr/ends-block\.bin' \
+    --log-found 'NUL byte in response header, response dropped: .*/nulhdr/cookie\.bin' \
+    --log-found 'NUL byte in response header, response dropped: .*/nulhdr/status\.bin' \
+    --errors 4 \
+    httrack 'BASEURL/nulhdr/index.html'
diff --git a/tests/local-server.py b/tests/local-server.py
index 546ef45a2..89e74ccf6 100755
--- a/tests/local-server.py
+++ b/tests/local-server.py
@@ -4076,7 +4076,61 @@ def route_warc100_normal(self):
         except OSError:
             pass
 
+    # A NUL inside a response header (RFC 9110 5.5) must drop the response.
+    # Each file is (status line, header lines, body); a None status line sends
+    # the body alone, as a server that answers without headers does.
+    NULHDR_BODY = b"0123456789abcdef"
+    NULHDR_OK = b"HTTP/1.1 200 OK"
+    NULHDR_FILES = {
+        "clean.bin": (NULHDR_OK, (b"Set-Cookie: good=1; Path=/",), NULHDR_BODY),
+        "body-nul.bin": (NULHDR_OK, (), b"\0" * 16),
+        "in-list.bin": (NULHDR_OK, (b"Content-Length: 16\0, 8",), NULHDR_BODY),
+        "ends-block.bin": (
+            NULHDR_OK,
+            (b"Content-Length: 16\0", b"Content-Length: 8"),
+            NULHDR_BODY,
+        ),
+        "cookie.bin": (
+            NULHDR_OK,
+            (b"Set-Cookie: nulcookie=1; Path=/", b"X-Pad: a\0b"),
+            NULHDR_BODY,
+        ),
+        "status.bin": (b"HTTP/1.1 200 OK\0junk", (), NULHDR_BODY),
+        "bare.html": (None, (), b"<html><body>bare-ok\0x</body></html>\n\n"),
+    }
+
+    def route_nulhdr_index(self):
+        self.send_html(
+            "".join('<a href="%s">%s</a>\n' % (n, n) for n in self.NULHDR_FILES)
+        )
+
+    def route_nulhdr_file(self):
+        status, lines, body = self.NULHDR_FILES[self.path.rsplit("/", 1)[1]]
+        self.close_connection = True
+        head = b""
+        if status is not None:
+            head = status + b"\r\nContent-Type: application/octet-stream\r\n"
+            if not any(line.startswith(b"Content-Length:") for line in lines):
+                head += b"Content-Length: %d\r\n" % len(body)
+            head += b"".join(line + b"\r\n" for line in lines)
+            head += b"Connection: close\r\n\r\n"
+        try:
+            self.wfile.write(head)
+            if self.command != "HEAD":
+                self.wfile.write(body)
+            self.wfile.flush()
+        except OSError:
+            pass
+
     ROUTES = {
+        "/nulhdr/index.html": route_nulhdr_index,
+        "/nulhdr/clean.bin": route_nulhdr_file,
+        "/nulhdr/in-list.bin": route_nulhdr_file,
+        "/nulhdr/ends-block.bin": route_nulhdr_file,
+        "/nulhdr/body-nul.bin": route_nulhdr_file,
+        "/nulhdr/cookie.bin": route_nulhdr_file,
+        "/nulhdr/status.bin": route_nulhdr_file,
+        "/nulhdr/bare.html": route_nulhdr_file,
         "/sfmark.html": route_singlefile_mark,
         "/warc100/index.html": route_warc100_index,
         "/warc100/interim.html": route_warc100_interim,