diff --git a/include/villas/formats/protobuf.hpp b/include/villas/formats/protobuf.hpp
index 9b33bee5d..ee7e3804a 100644
--- a/include/villas/formats/protobuf.hpp
+++ b/include/villas/formats/protobuf.hpp
@@ -7,13 +7,8 @@
 
 #pragma once
 
-#include <cstdlib>
-
 #include <villas/format.hpp>
 
-// Generated message descriptors by protoc
-#include <villas/formats/villas.pb-c.h>
-
 namespace villas {
 namespace node {
 
@@ -22,9 +17,6 @@ struct Sample;
 
 class ProtobufFormat : public BinaryFormat {
 
-protected:
-  enum SignalType detect(const Villas__Node__Value *val);
-
 public:
   using BinaryFormat::BinaryFormat;
 
diff --git a/lib/formats/protobuf.cpp b/lib/formats/protobuf.cpp
index 5000fbb9c..c34913bcc 100644
--- a/lib/formats/protobuf.cpp
+++ b/lib/formats/protobuf.cpp
@@ -11,9 +11,12 @@
 #include <villas/signal.hpp>
 #include <villas/utils.hpp>
 
+// Generated message descriptors by protoc
+#include <villas/formats/villas.pb-c.h>
+
 using namespace villas::node;
 
-enum SignalType ProtobufFormat::detect(const Villas__Node__Value *val) {
+static enum SignalType detect(const Villas__Node__Value *val) {
   switch (val->value_case) {
   case VILLAS__NODE__VALUE__VALUE_F:
     return SignalType::FLOAT;