diff --git a/common/rfb/LogWriter.h b/common/rfb/LogWriter.h
index 69b530c..104a875 100644
--- a/common/rfb/LogWriter.h
+++ b/common/rfb/LogWriter.h
@@ -36,9 +36,9 @@
 // is assigned a particular log level.
 
 #define DEF_LOGFUNCTION(name, level) \
-  inline void v##name(const char* fmt, va_list ap) { \
-    if (m_log && (level <= m_level))       \
-      m_log->write(level, m_name, fmt, ap);\
+  inline void v##name(const char* fmt, va_list ap) __printf_attr(2, 0) { \
+    if (m_log && (level <= m_level))        \
+      m_log->write(level, m_name, fmt, ap); \
   } \
   inline void name(const char* fmt, ...) __printf_attr(2, 3) { \
     if (m_log && (level <= m_level)) {     \