diff --git a/Core/include/Acts/Utilities/GridAccessHelpers.hpp b/Core/include/Acts/Utilities/GridAccessHelpers.hpp
index fbaf7f3acbd..df8f46ed39b 100644
--- a/Core/include/Acts/Utilities/GridAccessHelpers.hpp
+++ b/Core/include/Acts/Utilities/GridAccessHelpers.hpp
@@ -212,7 +212,7 @@ class LocalSubspace : public IBoundToGridLocal {
   }
 };
 
-class BoundCylinderToZPhi final : public IBoundToGridLocal {
+class BoundCylinderToZPhi : public IBoundToGridLocal {
  public:
   double radius = 1.;
   double shift = 0.;
diff --git a/Plugins/Json/src/GridJsonConverter.cpp b/Plugins/Json/src/GridJsonConverter.cpp
index 7b0bab73675..478224bc163 100644
--- a/Plugins/Json/src/GridJsonConverter.cpp
+++ b/Plugins/Json/src/GridJsonConverter.cpp
@@ -439,6 +439,11 @@ nlohmann::json Acts::GridAccessJsonConverter::toJson(
     jBoundToGridLocal["shift"] = boundCylinderToZPhi->shift;
   }
 
+  if (jBoundToGridLocal.empty()) {
+    throw std::invalid_argument(
+        "GridAccessJsonConverter: boundToGridLocal type not supported.");
+  }
+
   return jBoundToGridLocal;
 }