diff --git a/python/src/core/contractors/codac2_py_CtcDeriv.cpp b/python/src/core/contractors/codac2_py_CtcDeriv.cpp
index b67a504b1..45ca04137 100644
--- a/python/src/core/contractors/codac2_py_CtcDeriv.cpp
+++ b/python/src/core/contractors/codac2_py_CtcDeriv.cpp
@@ -27,7 +27,12 @@ void export_contract(py::class_<CtcDeriv>& exported)
   exported
 
     .def("contract",
-        [](const CtcDeriv& ctc, Slice<T>& x, const Slice<T>& v, const std::vector<Index_type>& ctc_indices)
+        // ctc_indices is read only by the if constexpr branch taken for
+        // IntervalVector; in the Interval instantiation that branch is
+        // discarded and the parameter goes unread, which MSVC /W4 reports as
+        // C4100. It cannot be dropped -- pybind11 takes the Python signature
+        // from this lambda, and the argument is exposed just below.
+        [](const CtcDeriv& ctc, Slice<T>& x, const Slice<T>& v, [[maybe_unused]] const std::vector<Index_type>& ctc_indices)
         -> py::tuple
         {
           if constexpr(std::is_same_v<T,IntervalVector>)
@@ -44,7 +49,9 @@ void export_contract(py::class_<CtcDeriv>& exported)
       "x"_a, "v"_a, "ctc_indices"_a = std::vector<Index>())
 
     .def("contract",
-        [](const CtcDeriv& ctc, SlicedTube<T>& x, const SlicedTube<T>& v, const std::vector<Index_type>& ctc_indices)
+        // Same as above: unread in the Interval instantiation, kept for the
+        // Python signature.
+        [](const CtcDeriv& ctc, SlicedTube<T>& x, const SlicedTube<T>& v, [[maybe_unused]] const std::vector<Index_type>& ctc_indices)
         -> py::tuple
         {
           if constexpr(std::is_same_v<T,IntervalVector>)
diff --git a/src/graphics/styles/codac2_StylePropertiesBase.cpp b/src/graphics/styles/codac2_StylePropertiesBase.cpp
index 07552fd8c..76e66240b 100644
--- a/src/graphics/styles/codac2_StylePropertiesBase.cpp
+++ b/src/graphics/styles/codac2_StylePropertiesBase.cpp
@@ -7,6 +7,7 @@
  *  \license    GNU Lesser General Public License (LGPL)
  */
 
+#include <iostream>
 #include "codac2_StylePropertiesBase.h"
 
 using namespace std;
@@ -35,6 +36,7 @@ void StylePropertiesBase::parse_parameter(const std::string& param)
       }
       catch (const std::invalid_argument& e)
       {
+        std::cerr << "codac2: invalid line width value \"" << param.substr(2) << "\": " << e.what() << std::endl;
         assert_release_constexpr(false && "Invalid line width value");
       }
     }
@@ -47,6 +49,7 @@ void StylePropertiesBase::parse_parameter(const std::string& param)
       }
       catch (const std::invalid_argument& e)
       {
+        std::cerr << "codac2: invalid z-value \"" << param.substr(2) << "\": " << e.what() << std::endl;
         assert_release_constexpr(false && "Invalid z-value");
       }
     }