diff --git a/runtime/el_runtime.c b/runtime/el_runtime.c
index 4d2874e..1356ae8 100644
--- a/runtime/el_runtime.c
+++ b/runtime/el_runtime.c
@@ -1961,6 +1961,13 @@ el_val_t http_response(el_val_t status, el_val_t headers_json, el_val_t body) {
     const char* b = EL_CSTR(body);
     if (!b) b = "";
 
+    /* Clear the fs_read binary-length hint: the envelope we're about to build
+     * is a fresh JSON string, not the raw file bytes.  Without this reset,
+     * http_worker would use the stale _tl_fs_read_len (= original file size)
+     * to copy the response — truncating the larger envelope before it reaches
+     * http_send_response and http_parse_envelope.                            */
+    _tl_fs_read_len = 0;
+
     JsonBuf out; jb_init(&out);
     jb_puts(&out, EL_HTTP_RESPONSE_TAG);  /* {"el_http_response":1 */
     jb_puts(&out, ",\"status\":");