diff --git a/docs/jpsi2ksp.ipynb b/docs/jpsi2ksp.ipynb
index 7f06e26a..bd6891d9 100644
--- a/docs/jpsi2ksp.ipynb
+++ b/docs/jpsi2ksp.ipynb
@@ -299,13 +299,10 @@
     "    s = _get_mandelstam_s(decay_chain)\n",
     "    parameter_defaults = {}\n",
     "    production_ff, new_pars = _create_form_factor(s, production_node)\n",
-    "    _is_messed_up(new_pars)\n",
     "    parameter_defaults.update(new_pars)\n",
     "    decay_ff, new_pars = _create_form_factor(s, decay_node)\n",
-    "    _is_messed_up(new_pars)\n",
     "    parameter_defaults.update(new_pars)\n",
     "    breit_wigner, new_pars = _create_breit_wigner(s, decay_node)\n",
-    "    _is_messed_up(new_pars)\n",
     "    parameter_defaults.update(new_pars)\n",
     "    return (\n",
     "        production_ff * decay_ff * breit_wigner,\n",
@@ -313,12 +310,6 @@
     "    )\n",
     "\n",
     "\n",
-    "def _is_messed_up(parameter_defaults):\n",
-    "    for key in parameter_defaults:\n",
-    "        if key.name == \"m0\" and not key.is_nonnegative:\n",
-    "            raise ValueError\n",
-    "\n",
-    "\n",
     "def _create_form_factor(\n",
     "    s: sp.Symbol, isobar: IsobarNode\n",
     ") -> tuple[sp.Expr, dict[sp.Symbol, float]]:\n",