diff --git a/libavformat/rtmpproto.c b/libavformat/rtmpproto.c
index 79af6de0e0..ac255661f6 100644
--- a/libavformat/rtmpproto.c
+++ b/libavformat/rtmpproto.c
@@ -1164,6 +1164,10 @@ static int rtmp_calc_swfhash(URLContext *s)
     if (!memcmp(in_data, "CWS", 3)) {
 #if CONFIG_ZLIB
         int64_t out_size;
+        if (in_size < 8) {
+            ret = AVERROR_INVALIDDATA;
+            goto fail;
+        }
         /* Decompress the SWF player file using Zlib. */
         if (!(out_data = av_malloc(8))) {
             ret = AVERROR(ENOMEM);