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)) {     \
diff --git a/common/rfb/Logger.h b/common/rfb/Logger.h
index e53764b..b75594c 100644
--- a/common/rfb/Logger.h
+++ b/common/rfb/Logger.h
@@ -28,6 +28,12 @@
 // and is attached to a particular Logger instance and
 // is assigned a particular log level.
 
+#ifdef __GNUC__
+#  define __printf_attr(a, b) __attribute__((__format__ (__printf__, a, b)))
+#else
+#  define __printf_attr(a, b)
+#endif // __GNUC__
+
 namespace rfb {
 
   class Logger {
@@ -45,7 +51,7 @@
     // -=- Write data to a log
 
     virtual void write(int level, const char *logname, const char *text) = 0;
-    void write(int level, const char *logname, const char* format, va_list ap);
+    void write(int level, const char *logname, const char* format, va_list ap) __printf_attr(4, 0);
 
     // -=- Register a logger