diff --git a/block/qcow2.c b/block/qcow2.c
index ad46c03c2f6daef22f5232d1df9c119c8bfc180d..8c60a6f06123c154da9f7768ee04ea6a2e857286 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -182,7 +182,8 @@ static void cleanup_unknown_header_ext(BlockDriverState *bs)
     }
 }
 
-static void report_unsupported(BlockDriverState *bs, const char *fmt, ...)
+static void GCC_FMT_ATTR(2, 3) report_unsupported(BlockDriverState *bs,
+    const char *fmt, ...)
 {
     char msg[64];
     va_list ap;