diff --git a/libavformat/flvenc.c b/libavformat/flvenc.c
index 7e410e627e..a7d4fa46a2 100644
--- a/libavformat/flvenc.c
+++ b/libavformat/flvenc.c
@@ -231,6 +231,9 @@ static void put_amf_string(AVIOContext *pb, const char *str)
 {
     size_t len = strlen(str);
     avio_wb16(pb, len);
+    // Avoid avio_write() if put_amf_string(pb, "") is inlined.
+    if (av_builtin_constant_p(len == 0) && len == 0)
+        return;
     avio_write(pb, str, len);
 }