diff --git a/waftools/fragments/libavfilter.c b/waftools/fragments/libavfilter.c
index b1a4175df4..ae9b96e81e 100644
--- a/waftools/fragments/libavfilter.c
+++ b/waftools/fragments/libavfilter.c
@@ -1,6 +1,5 @@
 #include <libavfilter/avfilter.h>
-void vf_next_query_format(void);
-void vf_next_query_format() {}
+static void vf_next_query_format() {}
 int main(void) {
     avfilter_register_all();
     vf_next_query_format();