diff --git a/src/arima.cpp b/src/arima.cpp
index b687dd6f5..85347318e 100644
--- a/src/arima.cpp
+++ b/src/arima.cpp
@@ -4,6 +4,7 @@
 #include <cmath>
 #include <span>
 #include <vector>
+#include <stdexcept>
 
 #include <pybind11/numpy.h>
 #include <pybind11/pybind11.h>
@@ -136,7 +137,14 @@ arima_css(const py::array_t<double> yv, const py::array_t<int32_t> armav,
 
   py::array_t<double> residv(n);
   const auto resid = make_span(residv);
+  if (static_cast<size_t>(ncond) > resid.size()) {
+     throw std::logic_error(
+       "Internal error: resid length (" + std::to_string(resid.size()) +
+       ") must be >= ncond (" + std::to_string(ncond) + ")"
+     );
+  }
   std::fill_n(resid.begin(), ncond, 0.0);
+
   std::vector<double> w(y.begin(), y.end());
 
   for (size_t _ = 0; _ < d; ++_) {