diff --git a/include/podio/LinkCollection.h b/include/podio/LinkCollection.h
index 81598e87d..3fccbf5d1 100644
--- a/include/podio/LinkCollection.h
+++ b/include/podio/LinkCollection.h
@@ -11,14 +11,14 @@
 /// Main macro for declaring links. Takes care of registering the necessary
 /// buffer creation functionality with the CollectionBufferFactory.
 #define PODIO_DECLARE_LINK(FromT, ToT)                                                                                 \
-  const static auto PODIO_PP_CONCAT(REGISTERED_LINK_, __COUNTER__) =                                                   \
+  const static auto PODIO_PP_CONCAT(REGISTERED_LINK_, __LINE__) =                                                      \
       podio::detail::registerLinkCollection<FromT, ToT>(podio::LinkCollection<FromT, ToT>::typeName);
 
 #if PODIO_ENABLE_SIO && __has_include("podio/detail/LinkSIOBlock.h")
   #include <podio/detail/LinkSIOBlock.h>
   /// Macro for registering the necessary SIOBlock for a Link with the SIOBlock factory
   #define PODIO_DECLARE_LINK_SIO(FromT, ToT)                                                                           \
-    const static auto PODIO_PP_CONCAT(LINK_SIO_BLOCK_, __COUNTER__) = podio::LinkSIOBlock<FromT, ToT>{};
+    const static auto PODIO_PP_CONCAT(LINK_SIO_BLOCK_, __LINE__) = podio::LinkSIOBlock<FromT, ToT>{};
 #endif
 
 #endif // PODIO_LINKCOLLECTION_H
diff --git a/tests/unittests/CMakeLists.txt b/tests/unittests/CMakeLists.txt
index f3487a16c..6f595b2ec 100644
--- a/tests/unittests/CMakeLists.txt
+++ b/tests/unittests/CMakeLists.txt
@@ -33,11 +33,20 @@ if(NOT Catch2_FOUND)
 
   # Reset the flags
   set(CMAKE_CXX_FLAGS ${CXX_FLAGS_CMAKE_USED})
+else()
+  # Same hack as above for the system-installed Catch2: mark its include
+  # directories as SYSTEM to suppress warnings from Catch2 headers
+  get_target_property(CATCH2_IF_INC_DIRS Catch2::Catch2 INTERFACE_INCLUDE_DIRECTORIES)
+  set_target_properties(Catch2::Catch2 PROPERTIES INTERFACE_SYSTEM_INCLUDE_DIRECTORIES "${CATCH2_IF_INC_DIRS}")
 endif()
 
 find_package(Threads REQUIRED)
 add_executable(unittest_podio unittest.cpp frame.cpp buffer_factory.cpp interface_types.cpp std_interoperability.cpp links.cpp)
 target_link_libraries(unittest_podio PUBLIC TestDataModel ExtensionDataModel InterfaceExtensionDataModel PRIVATE Catch2::Catch2WithMain Threads::Threads podio::podioRootIO)
+# Catch2 TEST_CASE/SECTION macros expand __COUNTER__ at the call site in user
+# code, so marking Catch2 headers as system includes is not sufficient to
+# suppress this warning, present with Clang 22
+target_compile_options(unittest_podio PRIVATE -Wno-c2y-extensions)
 if (ENABLE_SIO)
   target_link_libraries(unittest_podio PRIVATE podio::podioSioIO)
 endif()