diff --git a/log.c b/log.c
index 7acbd019..348b6db4 100644
--- a/log.c
+++ b/log.c
@@ -40,7 +40,8 @@
 /* #define REPMGR_DEBUG */
 
 static int	detect_log_facility(const char *facility);
-static void _stderr_log_with_level(const char *level_name, int level, const char *fmt, va_list ap);
+static void _stderr_log_with_level(const char *level_name, int level, const char *fmt, va_list ap)
+__attribute__((format(PG_PRINTF_ATTRIBUTE, 3, 0)));
 
 int			log_type = REPMGR_STDERR;
 int			log_level = LOG_NOTICE;
@@ -48,7 +49,7 @@ int			last_log_level = LOG_NOTICE;
 int			verbose_logging = false;
 int			terse_logging = false;
 
-void
+extern void
 stderr_log_with_level(const char *level_name, int level, const char *fmt, ...)
 {
 	va_list		arglist;
diff --git a/log.h b/log.h
index 8d1cf10f..e717be98 100644
--- a/log.h
+++ b/log.h
@@ -25,7 +25,7 @@
 #define REPMGR_SYSLOG 1
 #define REPMGR_STDERR 2
 
-void
+extern void
 stderr_log_with_level(const char *level_name, int level, const char *fmt,...)
 __attribute__((format(PG_PRINTF_ATTRIBUTE, 3, 4)));
 
@@ -123,8 +123,10 @@ bool		logger_shutdown(void);
 void		logger_set_verbose(void);
 void		logger_set_terse(void);
 
-void		log_hint(const char *fmt, ...);
-void		log_verbose(int level, const char *fmt, ...);
+void		log_hint(const char *fmt, ...)
+__attribute__((format(PG_PRINTF_ATTRIBUTE, 1, 2)));
+void		log_verbose(int level, const char *fmt, ...)
+__attribute__((format(PG_PRINTF_ATTRIBUTE, 2, 3)));
 
 extern int	log_type;
 extern int	log_level;