diff --git a/packages/bun-usockets/src/node_quic_shim.c b/packages/bun-usockets/src/node_quic_shim.c
index 05de1583669a..c1d55c09b3e3 100644
--- a/packages/bun-usockets/src/node_quic_shim.c
+++ b/packages/bun-usockets/src/node_quic_shim.c
@@ -294,19 +294,27 @@ const char *us_nq_hset_pairs(void *hset, size_t *len) {
 }
 void us_nq_hset_free(void *hset) { nq_hsi_discard_header_set(hset); }
 
-#define US_NQ_MAX_HEADERS 128
+/* Stack allocation covers node's default maxHeaderPairs; above that we
+ * spill to the heap. maxHeaderPairs is an inbound decoder limit only
+ * (node/src/quic/application.cc), so the encoder path imposes no policy cap. */
+#define US_NQ_STACK_HEADERS 128
 int us_nq_stream_send_headers(lsquic_stream_t *s, const char *buf, size_t len,
                               int expected, int eos) {
-    struct lsxpack_header hdrs[US_NQ_MAX_HEADERS];
-    int count = 0;
+    struct lsxpack_header stack_hdrs[US_NQ_STACK_HEADERS];
+    struct lsxpack_header *hdrs = stack_hdrs;
+    int count = 0, rv = -1;
     size_t i = 0;
-    if (expected < 0 || expected > US_NQ_MAX_HEADERS) return -1;
+    if (expected < 0) return -1;
+    if (expected > US_NQ_STACK_HEADERS) {
+        hdrs = malloc((size_t) expected * sizeof(*hdrs));
+        if (!hdrs) return -1;
+    }
     while (i < len) {
         /* The caller's pair count is authoritative: latin1 encoding of the
          * NUL-joined buffer maps U+0100-style code points onto the delimiter,
          * which would otherwise splice extra headers out of one user value
          * (node/src/node_http_common-inl.h bails the same way on n >= count_). */
-        if (count >= expected) return -1;
+        if (count >= expected) goto done;
         size_t name_off = i;
         while (i < len && buf[i]) i++;
         size_t name_len = i - name_off;
@@ -318,19 +326,25 @@ int us_nq_stream_send_headers(lsquic_stream_t *s, const char *buf, size_t len,
         if (i >= len) break;
         i++;
         unsigned char flags = (i < len) ? (unsigned char) buf[i++] : 0;
-        if (name_len > LSXPACK_MAX_STRLEN || val_len > LSXPACK_MAX_STRLEN)
-            return -1;
-        lsxpack_header_set_offset2(&hdrs[count], buf, name_off, name_len,
-                                   val_off, val_len);
+        if (name_len >= LSXPACK_MAX_STRLEN || val_len > LSXPACK_MAX_STRLEN)
+            goto done;
+        /* Per-entry base keeps val_offset (= name_len+1) under the setter's
+         * LSXPACK_MAX_STRLEN assert no matter how large the joined buffer is. */
+        lsxpack_header_set_offset2(&hdrs[count], buf + name_off, 0, name_len,
+                                   val_off - name_off, val_len);
         if (flags & 1) {
             hdrs[count].flags = LSXPACK_NEVER_INDEX;
             hdrs[count].indexed_type = 2;
         }
         count++;
     }
-    if (count != expected) return -1;
-    lsquic_http_headers_t list = { count, hdrs };
-    return lsquic_stream_send_headers(s, &list, eos);
+    if (count == expected) {
+        lsquic_http_headers_t list = { count, hdrs };
+        rv = lsquic_stream_send_headers(s, &list, eos);
+    }
+done:
+    if (hdrs != stack_hdrs) free(hdrs);
+    return rv;
 }
 
 static const struct lsquic_stream_if nq_stream_if = {
diff --git a/src/runtime/node/quic/stream.rs b/src/runtime/node/quic/stream.rs
index efaf487591e2..32e091afc5df 100644
--- a/src/runtime/node/quic/stream.rs
+++ b/src/runtime/node/quic/stream.rs
@@ -226,13 +226,15 @@ impl QuicStream {
             let _ = s.set_http_prio(urgency, incremental);
         }
         for (bytes, count, eos) in self.pending_headers.with_mut(core::mem::take) {
-            self.wrote_to_lsquic.set(true);
-            if s.send_headers(&bytes, count, eos) == 0 && eos {
-                self.with_state(|st| {
-                    st.fin_sent = 1;
-                    st.write_ended = 1;
-                });
-                s.shutdown(1);
+            if s.send_headers(&bytes, count, eos) == 0 {
+                self.wrote_to_lsquic.set(true);
+                if eos {
+                    self.with_state(|st| {
+                        st.fin_sent = 1;
+                        st.write_ended = 1;
+                    });
+                    s.shutdown(1);
+                }
             }
         }
         if uni {
diff --git a/test/js/node/quic/quic-stream.test.ts b/test/js/node/quic/quic-stream.test.ts
index 1bc9d9e2cdd1..fae192c744d7 100644
--- a/test/js/node/quic/quic-stream.test.ts
+++ b/test/js/node/quic/quic-stream.test.ts
@@ -178,4 +178,84 @@ describe("HTTP/3 header encoding", () => {
     expect(seen.length).toBe(1);
     expect(Object.keys(seen[0])).not.toContain("authorization");
   });
+
+  // `application.maxHeaderPairs` is an inbound decoder limit; the outbound
+  // encoder path must not impose its own cap. Before the fix, the shim's
+  // stack buffer rejected any block with >128 field lines, sendHeaders()
+  // returned false, nothing went on the wire, and the request hung until the
+  // idle timeout tore down the whole connection.
+  test("encodes a HEADERS block with more than 128 field lines", async () => {
+    const CUSTOM = 200;
+    // Long enough that the NUL-joined encode buffer runs well past 64KB,
+    // exercising the per-entry lsxpack_header base (not just the count path).
+    const VAL = Buffer.alloc(400, "a").toString();
+    const app = { maxHeaderPairs: 1024, maxHeaderLength: 1 << 20 };
+    const serverSaw = Promise.withResolvers<Record<string, string>>();
+    const serverSendOk = Promise.withResolvers<boolean>();
+    await using server = await listen(
+      async serverSession => {
+        serverSession.onstream = (stream: any) => {
+          stream.closed.catch(() => {});
+        };
+        await serverSession.closed.catch(() => {});
+      },
+      {
+        sni: { "*": { keys: [key], certs: [cert] } },
+        application: app,
+        transportParams: { maxIdleTimeout: 1 },
+        onheaders(this: any, headers: Record<string, string>) {
+          serverSaw.resolve(headers);
+          const resp: Record<string, string> = { ":status": "200" };
+          for (let i = 0; i < CUSTOM; i++) resp["x-resp-" + i] = String(i);
+          serverSendOk.resolve(this.sendHeaders(resp));
+          this.writer.endSync();
+        },
+      },
+    );
+
+    // A fresh endpoint so this test's `application` options reach the lsquic
+    // engine rather than whatever an earlier `connect()` in this file built.
+    const client = await connect(server.address, {
+      endpoint: {},
+      servername: "localhost",
+      verifyPeer: "manual",
+      application: app,
+      transportParams: { maxIdleTimeout: 1 },
+    });
+    await client.opened;
+
+    const req: Record<string, string> = {
+      ":method": "GET",
+      ":path": "/",
+      ":scheme": "https",
+      ":authority": "localhost",
+    };
+    for (let i = 0; i < CUSTOM; i++) req["x-req-" + i] = VAL;
+
+    const gotHeaders = Promise.withResolvers<Record<string, string>>();
+    const stream = await client.createBidirectionalStream({
+      onheaders(headers: Record<string, string>) {
+        gotHeaders.resolve(headers);
+      },
+    });
+    stream.closed.catch(gotHeaders.reject);
+    expect(stream.sendHeaders(req, { terminal: true })).toBe(true);
+
+    const seen = await serverSaw.promise;
+    expect(Object.keys(seen)).toHaveLength(CUSTOM + 4);
+    expect(seen["x-req-0"]).toBe(VAL);
+    expect(seen["x-req-" + (CUSTOM - 1)]).toBe(VAL);
+    // Server direction too: more than 128 response headers.
+    expect(await serverSendOk.promise).toBe(true);
+
+    const resp = await gotHeaders.promise;
+    expect(resp[":status"]).toBe("200");
+    expect(Object.keys(resp)).toHaveLength(CUSTOM + 1);
+    expect(resp["x-resp-" + (CUSTOM - 1)]).toBe(String(CUSTOM - 1));
+
+    for await (const _ of stream) {
+    }
+    expect(client.destroyed).toBe(false);
+    client.close();
+  });
 });