diff --git a/include/villas/formats/column.hpp b/include/villas/formats/column.hpp
index b179379cc..7a4969a09 100644
--- a/include/villas/formats/column.hpp
+++ b/include/villas/formats/column.hpp
@@ -47,9 +47,11 @@ public:
 		separator(sep)
 	{ }
 
-	virtual void header(FILE *f, const struct vlist *sigs);
+	virtual
+	void header(FILE *f, const struct vlist *sigs);
 
-	virtual void parse(json_t *json);
+	virtual
+	void parse(json_t *json);
 };
 
 template <const char *name, const char *desc, int flags = 0, char delimiter = '\n', char separator = '\t'>
@@ -58,20 +60,25 @@ class ColumnLineFormatPlugin : public FormatFactory {
 public:
 	using FormatFactory::FormatFactory;
 
-	virtual Format * make()
+	virtual
+	Format * make()
 	{
 		return new ColumnLineFormat(flags, delimiter, separator);
 	}
 
 	/// Get plugin name
-	virtual std::string
-	getName() const
-	{ return name; }
+	virtual
+	std::string getName() const
+	{
+		return name;
+	}
 
 	/// Get plugin description
-	virtual std::string
-	getDescription() const
-	{ return desc; }
+	virtual
+	std::string getDescription() const
+	{
+		return desc;
+	}
 };
 
 } /* namespace node */
diff --git a/include/villas/formats/iotagent_ul.hpp b/include/villas/formats/iotagent_ul.hpp
index ee8373861..45ef07b19 100644
--- a/include/villas/formats/iotagent_ul.hpp
+++ b/include/villas/formats/iotagent_ul.hpp
@@ -33,7 +33,9 @@ namespace node {
 class IotAgentUltraLightFormat : public Format {
 
 protected:
+	virtual
 	int sprint(char *buf, size_t len, size_t *wbytes, const struct sample * const smps[], unsigned cnt);
+	virtual
 	int sscan(const char *buf, size_t len, size_t *rbytes, struct sample * const smps[], unsigned cnt);
 
 public:
diff --git a/include/villas/formats/json.hpp b/include/villas/formats/json.hpp
index 8c073763c..5ffda8906 100644
--- a/include/villas/formats/json.hpp
+++ b/include/villas/formats/json.hpp
@@ -40,10 +40,14 @@ protected:
 	json_t * packTimestamps(const struct sample *smp);
 	int unpackTimestamps(json_t *json_ts, struct sample *smp);
 
-	virtual int packSample(json_t **j, const struct sample *smp);
-	virtual int packSamples(json_t **j, const struct sample * const smps[], unsigned cnt);
-	virtual int unpackSample(json_t *json_smp, struct sample *smp);
-	virtual int unpackSamples(json_t *json_smps, struct sample * const smps[], unsigned cnt);
+	virtual
+	int packSample(json_t **j, const struct sample *smp);
+	virtual
+	int packSamples(json_t **j, const struct sample * const smps[], unsigned cnt);
+	virtual
+	int unpackSample(json_t *json_smp, struct sample *smp);
+	virtual
+	int unpackSamples(json_t *json_smps, struct sample * const smps[], unsigned cnt);
 
 	int dump_flags;
 
@@ -53,13 +57,18 @@ public:
 		dump_flags(0)
 	{ }
 
+	virtual
 	int sscan(const char *buf, size_t len, size_t *rbytes, struct sample * const smps[], unsigned cnt);
+	virtual
 	int sprint(char *buf, size_t len, size_t *wbytes, const struct sample * const smps[], unsigned cnt);
 
+	virtual
 	int print(FILE *f, const struct sample * const smps[], unsigned cnt);
+	virtual
 	int scan(FILE *f, struct sample * const smps[], unsigned cnt);
 
-	virtual void parse(json_t *json);
+	virtual
+	void parse(json_t *json);
 };
 
 } /* namespace node */
diff --git a/include/villas/formats/json_edgeflex.hpp b/include/villas/formats/json_edgeflex.hpp
index 290edb109..4e5476f15 100644
--- a/include/villas/formats/json_edgeflex.hpp
+++ b/include/villas/formats/json_edgeflex.hpp
@@ -30,7 +30,9 @@ namespace node {
 class JsonEdgeflexFormat : public JsonFormat {
 
 protected:
+	virtual
 	int packSample(json_t **j, const struct sample *smp);
+	virtual
 	int unpackSample(json_t *json_smp, struct sample *smp);
 
 public:
diff --git a/include/villas/formats/json_kafka.hpp b/include/villas/formats/json_kafka.hpp
index e3caf9010..0376dc26a 100644
--- a/include/villas/formats/json_kafka.hpp
+++ b/include/villas/formats/json_kafka.hpp
@@ -31,7 +31,9 @@ namespace node {
 class JsonKafkaFormat : public JsonFormat {
 
 protected:
+	virtual
 	int packSample(json_t **j, const struct sample *smp);
+	virtual
 	int unpackSample(json_t *json_smp, struct sample *smp);
 
 	const char * villasToKafkaType(enum SignalType vt);
@@ -41,7 +43,8 @@ protected:
 public:
 	JsonKafkaFormat(int fl);
 
-	virtual void parse(json_t *json);
+	virtual
+	void parse(json_t *json);
 };
 
 } /* namespace node */
diff --git a/include/villas/formats/json_reserve.hpp b/include/villas/formats/json_reserve.hpp
index 0fbb06ea1..e8a315bb8 100644
--- a/include/villas/formats/json_reserve.hpp
+++ b/include/villas/formats/json_reserve.hpp
@@ -30,7 +30,9 @@ namespace node {
 class JsonReserveFormat : public JsonFormat {
 
 protected:
+	virtual
 	int packSample(json_t **j, const struct sample *smp);
+	virtual
 	int unpackSample(json_t *json_smp, struct sample *smp);
 
 public:
diff --git a/include/villas/formats/line.hpp b/include/villas/formats/line.hpp
index 362779d56..ca569d4aa 100644
--- a/include/villas/formats/line.hpp
+++ b/include/villas/formats/line.hpp
@@ -55,18 +55,24 @@ public:
 	{ }
 
 	/** Print a header. */
-	virtual void header(FILE *f, const struct vlist *sigs)
+	virtual
+	void header(FILE *f, const struct vlist *sigs)
 	{
 		header_printed = true;
 	}
 
-	virtual int sprint(char *buf, size_t len, size_t *wbytes, const struct sample * const smps[], unsigned cnt);
-	virtual int sscan(const char *buf, size_t len, size_t *rbytes, struct sample * const smps[], unsigned cnt);
+	virtual
+	int sprint(char *buf, size_t len, size_t *wbytes, const struct sample * const smps[], unsigned cnt);
+	virtual
+	int sscan(const char *buf, size_t len, size_t *rbytes, struct sample * const smps[], unsigned cnt);
 
-	virtual int scan(FILE *f, struct sample * const smps[], unsigned cnt);
-	virtual int print(FILE *f, const struct sample * const smps[], unsigned cnt);
+	virtual
+	int scan(FILE *f, struct sample * const smps[], unsigned cnt);
+	virtual
+	int print(FILE *f, const struct sample * const smps[], unsigned cnt);
 
-	virtual void parse(json_t *json);
+	virtual
+	void parse(json_t *json);
 };
 
 template <typename T, const char *name, const char *desc, int flags = 0, char delimiter = '\n'>
@@ -75,20 +81,25 @@ class LineFormatPlugin : public FormatFactory {
 public:
 	using FormatFactory::FormatFactory;
 
-	virtual Format * make()
+	virtual
+	Format * make()
 	{
 		return new T(flags, delimiter);
 	}
 
 	/// Get plugin name
-	virtual std::string
-	getName() const
-	{ return name; }
+	virtual
+	std::string getName() const
+	{
+		return name;
+	}
 
 	/// Get plugin description
-	virtual std::string
-	getDescription() const
-	{ return desc; }
+	virtual
+	std::string getDescription() const
+	{
+		return desc;
+	}
 };
 
 } /* namespace node */
diff --git a/include/villas/formats/protobuf.hpp b/include/villas/formats/protobuf.hpp
index 02868a70a..0c81d491d 100644
--- a/include/villas/formats/protobuf.hpp
+++ b/include/villas/formats/protobuf.hpp
@@ -44,7 +44,9 @@ protected:
 public:
 	using BinaryFormat::BinaryFormat;
 
+	virtual
 	int sscan(const char *buf, size_t len, size_t *rbytes, struct sample * const smps[], unsigned cnt);
+	virtual
 	int sprint(char *buf, size_t len, size_t *wbytes, const struct sample * const smps[], unsigned cnt);
 };
 
diff --git a/include/villas/formats/raw.hpp b/include/villas/formats/raw.hpp
index 2b5274ce1..e87f1e23c 100644
--- a/include/villas/formats/raw.hpp
+++ b/include/villas/formats/raw.hpp
@@ -64,10 +64,13 @@ public:
 			flags |= (int) SampleFlags::HAS_SEQUENCE | (int) SampleFlags::HAS_TS_ORIGIN;
 	}
 
+	virtual
 	int sscan(const char *buf, size_t len, size_t *rbytes, struct sample * const smps[], unsigned cnt);
+	virtual
 	int sprint(char *buf, size_t len, size_t *wbytes, const struct sample * const smps[], unsigned cnt);
 
-	virtual void parse(json_t *json);
+	virtual
+	void parse(json_t *json);
 };
 
 class GtnetRawFormat : public RawFormat {
diff --git a/include/villas/formats/value.hpp b/include/villas/formats/value.hpp
index d27f34e8e..80293592c 100644
--- a/include/villas/formats/value.hpp
+++ b/include/villas/formats/value.hpp
@@ -35,7 +35,9 @@ class ValueFormat : public Format {
 public:
 	using Format::Format;
 
+	virtual
 	int sscan(const char *buf, size_t len, size_t *rbytes, struct sample * const smps[], unsigned cnt);
+	virtual
 	int sprint(char *buf, size_t len, size_t *wbytes, const struct sample * const smps[], unsigned cnt);
 };
 
diff --git a/include/villas/formats/villas_human.hpp b/include/villas/formats/villas_human.hpp
index 35f40042c..d98aa839f 100644
--- a/include/villas/formats/villas_human.hpp
+++ b/include/villas/formats/villas_human.hpp
@@ -33,12 +33,15 @@ namespace node {
 class VILLASHumanFormat : public LineFormat {
 
 protected:
+	virtual
 	size_t sprintLine(char *buf, size_t len, const struct sample *smp);
+	virtual
 	size_t sscanLine(const char *buf, size_t len, struct sample *smp);
 
 public:
 	using LineFormat::LineFormat;
 
+	virtual
 	void header(FILE *f, const struct vlist *sigs);
 };