diff --git a/src/shared/strv.h b/src/shared/strv.h
index 2dc2bc6c4..b356d034c 100644
--- a/src/shared/strv.h
+++ b/src/shared/strv.h
@@ -39,7 +39,7 @@ unsigned strv_length(char * const *l) _pure_;
 int strv_extend_strv(char ***a, char **b);
 int strv_extend_strv_concat(char ***a, char **b, const char *suffix);
 int strv_extend(char ***l, const char *value);
-int strv_extendf(char ***l, const char *format, ...);
+int strv_extendf(char ***l, const char *format, ...) _printf_(2,0);
 int strv_push(char ***l, char *value);
 int strv_consume(char ***l, char *value);