diff --git a/lib/compat/cpp-start.h b/lib/compat/cpp-start.h
index 4423ca8f36..c0c80864b1 100644
--- a/lib/compat/cpp-start.h
+++ b/lib/compat/cpp-start.h
@@ -91,6 +91,10 @@
 
 #ifdef __cplusplus
 
+#ifndef __STDC_VERSION__
+#define __STDC_VERSION__ 0
+#endif
+
 #define this this_
 
 extern "C" {
diff --git a/modules/grpc/otel/filterx/object-otel-kvlist.cpp b/modules/grpc/otel/filterx/object-otel-kvlist.cpp
index 8dccbf5d34..98ead65208 100644
--- a/modules/grpc/otel/filterx/object-otel-kvlist.cpp
+++ b/modules/grpc/otel/filterx/object-otel-kvlist.cpp
@@ -31,6 +31,9 @@
 #include <google/protobuf/reflection.h>
 #include <stdexcept>
 
+/* The deprecated MutableRepeatedPtrField() does not have a proper alternative. */
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+
 using namespace syslogng::grpc::otel::filterx;
 using opentelemetry::proto::common::v1::KeyValueList;
 using opentelemetry::proto::common::v1::AnyValue;
diff --git a/modules/grpc/protos/CMakeLists.txt b/modules/grpc/protos/CMakeLists.txt
index a4851d30cb..b234513942 100644
--- a/modules/grpc/protos/CMakeLists.txt
+++ b/modules/grpc/protos/CMakeLists.txt
@@ -91,5 +91,5 @@ target_include_directories(grpc-protos
   PRIVATE ${CMAKE_CURRENT_BINARY_DIR} ${PROJECT_SOURCE_DIR}
 )
 
-target_compile_options(grpc-protos PRIVATE -Wno-switch-default)
+target_compile_options(grpc-protos PRIVATE -Wno-switch-default -Wno-deprecated-declarations)
 install(TARGETS grpc-protos LIBRARY DESTINATION lib/syslog-ng COMPONENT grpc-protos)
diff --git a/modules/grpc/protos/Makefile.am b/modules/grpc/protos/Makefile.am
index 06f1805093..28a14f5570 100644
--- a/modules/grpc/protos/Makefile.am
+++ b/modules/grpc/protos/Makefile.am
@@ -117,6 +117,7 @@ modules_grpc_protos_libgrpc_protos_la_CXXFLAGS = \
   $(AM_CXXFLAGS) \
   $(PROTOBUF_CFLAGS) \
   $(GRPCPP_CFLAGS) \
+  -Wno-deprecated-declarations \
   -I$(GOOGLEAPIS_PROTO_SRCDIR) \
   -I$(GOOGLEAPIS_PROTO_BUILDDIR) \
   -I$(OPENTELEMETRY_PROTO_SRCDIR) \