diff --git a/src/Reporter.h b/src/Reporter.h
index 19cdbb7e82..85b9a483a2 100644
--- a/src/Reporter.h
+++ b/src/Reporter.h
@@ -66,11 +66,11 @@ public:
 
 	// Report a runtime error in evaluating a Bro script expression. This
 	// function will not return but raise an InterpreterException.
-	void ExprRuntimeError(const Expr* expr, const char* fmt, ...);
+	void ExprRuntimeError(const Expr* expr, const char* fmt, ...) __attribute__((format(printf, 3, 4)));
 
 	// Report a runtime error in evaluating a Bro script expression. This
 	// function will not return but raise an InterpreterException.
-	void RuntimeError(const Location* location, const char* fmt, ...);
+	void RuntimeError(const Location* location, const char* fmt, ...) __attribute__((format(printf, 3, 4)));
 
 	// Report a traffic weirdness, i.e., an unexpected protocol situation
 	// that may lead to incorrectly processing a connnection.
@@ -123,7 +123,7 @@ public:
 private:
 	void DoLog(const char* prefix, EventHandlerPtr event, FILE* out,
 		   Connection* conn, val_list* addl, bool location, bool time,
-		   const char* postfix, const char* fmt, va_list ap);
+		   const char* postfix, const char* fmt, va_list ap) __attribute__((format(printf, 10, 0)));
 
 	// The order if addl, name needs to be like that since fmt_name can
 	// contain format specifiers
diff --git a/src/input/Manager.h b/src/input/Manager.h
index e7a1ebe2d6..8296ce9f8b 100644
--- a/src/input/Manager.h
+++ b/src/input/Manager.h
@@ -240,7 +240,7 @@ private:
 
 	enum class ErrorType { INFO, WARNING, ERROR };
 	void ErrorHandler(const Stream* i, ErrorType et, bool reporter_send, const char* fmt, ...) __attribute__((format(printf, 5, 6)));
-	void ErrorHandler(const Stream* i, ErrorType et, bool reporter_send, const char* fmt, va_list ap);
+	void ErrorHandler(const Stream* i, ErrorType et, bool reporter_send, const char* fmt, va_list ap) __attribute__((format(printf, 5, 0)));
 
 	Stream* FindStream(const string &name);
 	Stream* FindStream(ReaderFrontend* reader);