diff --git a/src/htsbuf.h b/src/htsbuf.h
index 856f275b..13aaedb5 100644
--- a/src/htsbuf.h
+++ b/src/htsbuf.h
@@ -48,7 +48,8 @@ void htsbuf_queue_flush(htsbuf_queue_t *hq);
 
 void htsbuf_vqprintf(htsbuf_queue_t *hq, const char *fmt, va_list ap);
 
-void htsbuf_qprintf(htsbuf_queue_t *hq, const char *fmt, ...);
+void htsbuf_qprintf(htsbuf_queue_t *hq, const char *fmt, ...)
+  __attribute__((format(printf,2,3)));
 
 void htsbuf_append(htsbuf_queue_t *hq, const void *buf, size_t len);
 
diff --git a/src/tvheadend.h b/src/tvheadend.h
index cfa92fe0..31570147 100644
--- a/src/tvheadend.h
+++ b/src/tvheadend.h
@@ -359,9 +359,11 @@ static inline unsigned int tvh_strhash(const char *s, unsigned int mod)
 void tvh_str_set(char **strp, const char *src);
 int tvh_str_update(char **strp, const char *src);
 
-void tvhlog(int severity, const char *subsys, const char *fmt, ...);
+void tvhlog(int severity, const char *subsys, const char *fmt, ...)
+  __attribute__((format(printf,3,4)));
 
-void tvhlog_spawn(int severity, const char *subsys, const char *fmt, ...);
+void tvhlog_spawn(int severity, const char *subsys, const char *fmt, ...)
+  __attribute__((format(printf,3,4)));
 
 #define	LOG_EMERG	0	/* system is unusable */
 #define	LOG_ALERT	1	/* action must be taken immediately */